Methods for producing a paired tag from a nucleic acid sequence and methods of use thereof

ABSTRACT

Methods for producing a paired tag from a nucleic acid sequence are provided in which the paired tag comprises the 5′ end tag and 3′ end tag of the nucleic acid sequence. In one embodiment, the nucleic acid sequence comprises two restriction endonuclease recognition sites specific for a restriction endonuclease that cleaves the nucleic acid sequence distally to the restriction endonuclease recognition sites. In another embodiment, the nucleic acid sequence further comprises restriction endonuclease recognition sites specific for a rare cutting restriction endonuclease. Methods of using paired tags are also provided. In one embodiment, paired tags are used to characterize a nucleic acid sequence. In a particular embodiment, the nucleic acid sequence is a genome. In one embodiment, the characterization of a nucleic acid sequence is karyotyping. Alternatively, in another embodiment, the characterization of a nucleic acid sequence is mapping of the sequence. In a further embodiment, a method is provided for identifying nucleic acid sequences that encode at least two interacting proteins.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/516,080, filed Oct. 31, 2003.

The entire teachings of the above application are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Whole genome shotgun sequencing, assembly and finishing is typically thestrategy of choice for microbial and fungal genome sequencing. Thecost-advantages and simplicity of the whole genome approach relative toa BAC based or hybrid sequencing strategy argue strongly for itscontinued development and application in future sequencing projects.However, a major problem with the BAC-based approaches is the high costand operational burden associated with the production of 15,000-25,000individual BAC subclone libraries, the 15-20% waste associated withre-sequencing the vector, as well as the unavoidable E. colicontamination, the need to deal with transposon and bacteriophageinsertions, and the 20-50% waste in redundant sequencing of BACoverlaps. Although these costs can be reduced by sequencing the BACs atlow coverage (using a hybrid BAC/WGS strategy, for example) or by usinga pooling strategy, they cannot be eliminated. The need to generate aphysical map by using restriction digest fingerprinting or by complexpooling and sequence based mapping strategies adds additional cost andoperational overhead.

Thus, a need exists for more cost-efficient sequencing methods and forbetter methods of generating a reliable sequence-derived scaffold thatcan support the accurate selection of clones to finish any desiredregion of the genome with reduced operational burden, increasedefficiency, elimination of problems associated with transposon andbacteriophage insertions and reduction in wasted time, effort andexpense spent in redundant sequencing. Additionally, a need exists toprovide a reliable and efficient method that facilitates whole genomeassembly and/or karyotying of a genome, and which enables the reliableand efficient detection of sequence inversion in a genome.

Current bacterial and yeast two-hybrid screening methods are useful todiscover the identity of two interacting proteins. However, thesemethods suffer from the need for large numbers of transformations to beperformed: one for each bait to be analyzed against one or more preymolecule. Although some methods have been developed to permit pools often to one hundred baits to be screened in parallel, these methodsrequire additional handling steps to deconvolute the identities of theindividual baits. Therefore, these methods only incrementally increasethe efficiency of conventional two-hybrid systems.

Thus, a need exists for a method to increase the efficiency oftwo-hybrid systems for the identification of two interacting proteins.

SUMMARY OF THE INVENTION

The present invention provides a method for producing a paired tag froma nucleic acid sequence (also referred to herein as a nucleotidesequence), wherein at least one restriction endonuclease recognitionsite is present at the 5′ and 3′ end of the nucleic acid sequence andupon cleavage results in production a paired tag. In one embodiment thepresent invention provides a method for producing a paired tag from anucleic acid sequence, wherein two restriction endonuclease recognitionsites specific for a restriction endonuclease that cleaves the nucleicacid sequence fragment distally to the restriction endonucleaserecognition site are present at the 5′ and 3′ ends of the nucleic acidsequence, thereby producing a 5′ tag and a 3′ tag (a paired tag) fromthe nucleic acid sequence upon cleavage by the restriction endonuclease.

In another embodiment the present invention provides a method forproducing a paired tag from a nucleic acid sequence, wherein the nucleicacid sequence comprises one restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence on both sides of the recognition site.

In addition, the present invention provides a method for producing apaired tag from a nucleic acid sequence, wherein the nucleic acidsequence comprises two restriction endonuclease recognition sitesspecific for a restriction endonuclease that cleaves the nucleic acidsequence between the two recognition sites.

The present invention also provides a method for producing a paired tagfrom a nucleic acid sequence, wherein the nucleic acid sequencecomprises at least one linker, the at least one linker is joined to the5′ and 3′ ends of the nucleic acid sequence, wherein producing afragment on either or both sides of the linker produces a paired tagfrom the nucleic acid sequence.

The present invention also provides a method for producing a paired tagfrom a nucleic acid sequence, wherein the nucleic acid sequencecomprises at least one recombination site, wherein a recombination eventat this recombination site in the nucleic acid sequence produces apaired tag from the nucleic acid sequence.

Furthermore, the present invention provides methods of using a pairedtag to characterize a sequence and identify nucleic acid sequences thatencode at least two interacting proteins.

In one embodiment, the invention is directed to a method for producing apaired tag from a nucleic acid sequence, wherein the nucleic acidsequence comprises two restriction endonuclease recognition sitesspecific for a restriction endonuclease that cleaves the nucleic acidsequence distally to the restriction endonuclease recognition site,comprising the steps of cleaving the restriction endonucleaserecognition sites using the restriction endonuclease that is specificfor the restriction endonuclease recognition sites, thereby producing a5′ end tag and a 3′ end tag from the nucleic acid sequence and joiningthe 5′ end tag with the 3′ end tag from the nucleic acid sequence,thereby producing a paired tag from the nucleic acid sequence. In aparticular embodiment, the nucleic acid sequence further comprises atleast two restriction endonuclease recognition sites specific for a rarecutting restriction endonuclease.

In another embodiment of the invention, a method is provided forcharacterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence thereby producing a plurality ofnucleic acid sequence fragments having a 5′ end and a 3′ end, b)introducing into the 5′ end and into the 3′ end of each nucleic acidsequence fragment, (i) a restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, and (ii) a restriction endonuclease recognition site specific fora rare cutting restriction endonuclease, thereby producing modifiednucleic acid sequence fragments, c) cleaving the restrictionendonuclease recognition site specific for a rare cutting restrictionendonuclease in each modified nucleic acid sequence fragment with therare cutting restriction endonuclease, thereby producing a plurality ofnucleic acid sequence fragments having compatible ends, d) maintainingthe fragments having compatible ends under conditions in which thecompatible ends intramolecularly ligate, thereby producing a pluralityof circularized nucleic acid sequences comprising two restrictionendonuclease recognition sites specific for restriction endonucleasesthat cleave the nucleic acid sequence fragment distally to therestriction endonuclease recognition sites, e) cleaving the circularizednucleic acid sequences at the restriction endonuclease recognition siteswith the restriction endonucleases specific for the restrictionendonuclease recognition sites, thereby producing a plurality of pairedtags comprising a 5′ end tag and a 3′ end tag of the nucleic acidsequence fragment, and f) characterizing the paired tags, therebycharacterizing the nucleic acid sequence. In one embodiment, the nucleicacid sequence is a genome. In a further embodiment, the methodkaryotypes the genome.

The invention also provides in one embodiment, a method forcharacterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence thereby producing a plurality ofnucleic acid sequence fragments having a 5′ end and a 3′ end, b)introducing into the 5′ end and into the 3′ end of each nucleic acidsequence fragment a restriction endonuclease recognition site specificfor a restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site,thereby producing a plurality of modified nucleic acid sequencefragments, c) cloning the modified nucleic acid sequence fragments,thereby producing cloned nucleic acid sequence fragments, d) cleavingthe restriction endonuclease recognition sites at the 5′ end and the 3′end of the cloned nucleic acid sequence fragments using the restrictionendonuclease that is specific for the restriction endonucleaserecognition sites, thereby producing a 5′ end tag and a 3′ end tag ofeach cloned nucleic acid sequence fragment, e) joining the 5′ end tag tothe 3′ end tag of each cloned nucleic acid sequence fragment therebyproducing a plurality of paired tags; and f) characterizing the pairedtags, thereby characterizing the nucleic acid sequence.

In another aspect of the invention, provided herein is a method forcharacterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence thereby producing a plurality ofnucleic acid sequence fragments having a 5′ end and a 3′ end, b) cloningeach nucleic acid sequence fragment, wherein a restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site is introduced into the 5′ end and into the3′ end of each cloned nucleic acid sequence fragment, thereby producinga plurality of cloned nucleic acid sequence fragments, c) cleaving therestriction endonuclease recognition sites at the 5′ end and the 3′ endof each cloned nucleic acid sequence fragment using the restrictionendonuclease that is specific for the restriction endonucleaserecognition sites, thereby producing a 5′ end tag and a 3′ end tag ofthe cloned nucleic acid sequence fragments, d) joining the 5′ end tag tothe 3′ end tag of each cloned nucleic acid sequence fragment therebyproducing a plurality of paired tags, and e) characterizing the pairedtags, thereby characterizing the nucleic acid sequence.

In one embodiment of the invention, provided herein is a method forproducing a paired tag from a first nucleic acid sequence fragment,without cloning, comprising the steps of joining the 5′ and 3′ ends of anucleic acid sequence fragment via a linker such that the linker islocated between the 5′ end and the 3′ end of the first nucleic acidsequence fragment in a circular nucleic acid molecule, b) cleaving thecircular nucleic acid molecule, thereby producing a paired tag wherein a5′end tag of the first nucleic acid sequence fragment is joined to a 3′end tag of the first nucleic acid sequence fragment via the linker. Inone embodiment, the linker comprises at least two restrictionendonuclease recognition sites specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and the circular nucleic acidmolecule is cleaved with a restriction endonuclease that cleaves thenucleic acid sequence fragment distally to the restriction endonucleaserecognition site to thereby producing the paired tag. In a furtherembodiment, the restriction endonuclease recognition sites areimmediately adjacent to the ends of the first nucleic acid sequencefragment.

In a further embodiment of the invention, provided herein is a methodfor producing a paired tag from a first nucleic acid sequence fragment,without cloning, comprising the steps of a) joining the 5′ and 3′ends ofa first nucleic acid sequence fragment to at least one adapter, b)cleaving the adapter(s), thereby producing a second nucleic acidsequence fragment with compatible ends, c) circularizing the secondnucleic acid sequence fragment such that a 5′end of the first nucleicacid sequence fragment is joined to a 3′ end of the first nucleic acidsequence fragment via a linker derived from the adapter(s), therebyproducing a circular nucleic acid molecule, and cleaving the circularnucleic acid molecule, thereby producing a paired tag wherein a 5′endtag of the first nucleic acid sequence fragment is joined to a 3′ endtag of the first nucleic acid sequence fragment via the linker. In aparticular embodiment, the adapter comprises at least two restrictionendonuclease recognition sites specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, the adapter comprises arestriction endonuclease recognition site specific for a rare cuttingrestriction endonuclease, cleaving the adapter joined to the nucleicacid sequence fragment with a rare cutting restriction endonuclease toproduce the compatible ends, and cleaving the circular nucleic acidmolecule with a restriction endonuclease that cleaves distally to therestriction endonuclease recognition site. In a further embodiment, therestriction endonuclease recognition sites specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site are immediately adjacentto the 5′ and 3′ ends of the nucleic acid sequence fragment.

In another embodiment, provided herein is a method for producing apaired tag from a first nucleic acid sequence fragment, without cloning,comprising the steps of a) joining the 5′ and 3′ ends of a first nucleicacid sequence fragment via a first linker such that the first linker islocated between the 5′ end and the 3′ end of the first nucleic acidsequence fragment in a first circular nucleic acid molecule, b) cleavingthe first circular nucleic acid molecule, thereby producing a secondnucleic acid sequence fragment wherein a 5′end tag of the first nucleicacid sequence fragment is joined to a 3′ end tag of the first nucleicacid sequence fragment via the first linker, c) joining a second linkerto the 5′ and 3′ ends of the second nucleic acid sequence fragment, andd) amplifying the second nucleic acid fragment using an oligonucleotidecomplementary to a sequence present in the second linker.

In a further embodiment of the invention, provided herein is a methodfor producing a paired tag from a first nucleic acid sequence fragment,without cloning, comprising the steps of a) joining the 5′ and 3′ endsof a first nucleic acid sequence fragment via a first linker such thatthe first linker is located between the 5′ end and the 3′ end of thefirst nucleic acid sequence fragment in a first circular nucleic acidmolecule, b) cleaving the first circular nucleic acid molecule, therebyproducing a second nucleic acid sequence fragment wherein a 5′end tag ofthe first nucleic acid sequence fragment is joined to a 3′ end tag ofthe first nucleic acid sequence fragment via the first linker, c)joining the 5′ and 3′ ends of a second nucleic acid sequence fragmentvia a second linker such that the second linker is located between the5′ end and the 3′ end of the first nucleic acid sequence fragment in asecond circular nucleic acid molecule, and d) amplifying a nucleic acidsequence fragment from the second circular nucleic acid molecule usingtwo oligonucleotides complementary to sequences present in the secondlinker. In one embodiment, the second linker comprises a recognitionsite for a rare-cutting restriction endonuclease, and the secondcircular nucleic acid molecule is cleaved using a rare-cuttingrestriction endonuclease that recognizes the site in the second linker.In another embodiment, the first linker comprises at least tworestriction endonuclease recognition sites specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, and the first circularnucleic acid molecule is cleaved with a restriction endonuclease thatcleaves the nucleic acid sequence fragment distally to the restrictionendonuclease recognition site. In a particular embodiment, therestriction endonuclease recognition sites specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site are immediately adjacentto the ends of the first nucleic acid sequence fragment. Furthermore, inone embodiment, the second nucleic acid fragment is purified prior toamplification, for example by affinity capture using a reagent specificfor the first linker prior to amplification. In one example, the firstlinker comprises a biotin moiety, a sequence capable of forming a triplehelix, or a recognition site for a DNA binding protein.

In another embodiment of the invention, provided herein is a method forcharacterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence to produce a plurality of nucleicacid sequence fragments having a 5′ end and a 3′ end, b) joining one ormore first adapters to the 5′ and 3′ ends, wherein the one or more firstadapters are compatible for promoting intramolecular ligation, therebyproducing a plurality of modified nucleic acid sequence fragments,intramolecularly ligating the modified nucleic acid sequence fragmentsthereby producing a plurality of circularized nucleic acid sequences,wherein the one or more first adapters forms a linker between the 5′endand the 3′end of the circularized nucleic acid sequence fragment, c)fragmenting the circularized nucleic acid sequences by random shearingor by other means thereby producing linear fragments comprising thelinker and a paired tag comprising the 5′ end and a 3′ end of thenucleic acid sequence fragment, d) joining a second adapter to each ofthe 5′ and 3′ ends of the linear fragments to produce a plurality oflinear fragments having the second adapter at each 5′ and 3′ end, e)amplifying the linear fragments using a primer that is complementary tothe second adapter thereby amplifying the paired tags, and f)characterizing the paired tags, thereby characterizing the nucleic acidsequence.

In another aspect of the invention, provided herein is a method forcharacterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence to produce a plurality of nucleicacid sequence fragments each having a 5′ end and a 3′ end, b) joiningone or more first adapters to the 5′ and 3′ ends, wherein the one ormore first adapters are compatible for promoting intramolecularligation, thereby producing a first plurality of modified nucleic acidsequence fragments, intramolecularly ligating the modified nucleic acidsequence fragments thereby producing a first plurality of circularizednucleic acid sequences, wherein the one or more first adapters forms afirst linker between the 5′end and the 3′end of the circularized nucleicacid sequence fragment, c) fragmenting the circularized nucleic acidfragments by random shearing or by other means thereby producing linearfragments comprising the first linker and a paired tag comprising the 5′end and a 3′ end of the nucleic acid sequence fragment, d) joining asecond adapter to each of the 5′ and 3′ ends of the fragments to producea second plurality of modified fragments having the second adapter ateach 5′ and 3′ end, wherein the second adapter at the 5′ and 3′ ends arecompatible for promoting intramolecular ligation, intramolecularlyligating the second plurality of modified nucleic acid sequencefragments thereby producing a second plurality of circularized nucleicacid sequences, wherein the second adapter at each 5′ and 3′ end form asecond linker located between the 5′ and 3′ ends of the second pluralityof circularized nucleic acid sequences, and wherein the second linkercomprises two priming sites, f) amplifying the second plurality ofcircularized nucleic acid sequences using two different primers that arecomplementary to the priming sites in the second linker, therebyamplifying the paired tags, and g) characterizing the paired tags,thereby characterizing the nucleic acid sequence.

In an alternative aspect of the invention, provided herein is a methodfor characterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence to produce a plurality of nucleicacid sequence fragments having a 5′ end and a 3′ end, b) joining one ormore first adapters to the 5′ and 3′ ends, wherein the one or more firstadapters are compatible for promoting intramolecular ligation, therebyproducing a first plurality of modified nucleic acid sequence fragments,intramolecularly ligating the first plurality of modified nucleic acidsequence fragments thereby producing a first plurality of circularizednucleic acid sequences, wherein the one or more first adapters forms afirst linker between the 5′end and the 3′end of the circularized nucleicacid sequence fragment, c) fragmenting the first plurality ofcircularized nucleic acid sequences by random shearing or by othermeans, thereby producing first linear fragments comprising the firstlinker and a paired tag comprising the 5′ end and a 3′ end of thenucleic acid sequence fragment, d) joining one or more second adaptersto the each of the 5′ and 3′ ends of the first linear fragments, whereinthe one or more second adapters are compatible for promotingintramolecular ligation, thereby producing a second plurality ofmodified nucleic acid sequence fragments, and intramolecularly ligatingthe second plurality of modified nucleic acid sequence fragments toproduce a second plurality of circularized nucleic acid sequences,wherein the on or more second adapters form a second linker between the5′end and the 3′end of the second circularized nucleic acid sequencefragments, and wherein the second linker comprises two priming sitesseparated by a rare-cutting restriction endonuclease cleavage site, f)cleaving the second plurality of circularized nucleic acid sequencesusing a rare-cutting restriction endonuclease that recognizes thecleavage site in the second linker, thereby producing a second pluralityof linear fragments g) amplifying the second plurality of linearfragments using two different primers that are complementary to thepriming sites in the second linker, and h) characterizing the pairedtags, thereby characterizing the nucleic acid sequence.

In another aspect of the invention, provided herein is a method forcharacterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence to produce a plurality of nucleicacid sequence fragments having a 5′ end and a 3′ end, b) joining one ormore first adapters to the 5′ and 3′ ends, wherein the one or more firstadapters are compatible for promoting intramolecular ligation, therebyproducing a first plurality of modified nucleic acid sequence fragments,intramolecularly ligating the first plurality of modified nucleic acidsequence fragments thereby producing a first plurality of circularizednucleic acid sequences, wherein the one or more first adapters forms afirst linker between the 5′end and the 3′end of the circularized nucleicacid sequence fragment, and wherein the first linker comprises asequence or chemical moiety that enables isolation or separation (e.g.,by affinity capture), c) fragmenting the first plurality of circularizednucleic acid sequences by random shearing or by other means, therebyproducing linear fragments comprising the first linker and a paired tagcomprising the 5′ end and the 3′ end of the nucleic acid sequencefragment, d) purifying the linear fragments by affinity capture, e)joining one or more second adapters to the each of the 5′ and 3′ ends ofthe first linear fragments, wherein the one or more second adapters arecompatible for promoting intramolecular ligation, thereby producing asecond plurality of modified nucleic acid sequence fragments, andintramolecularly ligating the second plurality of modified nucleic acidsequence fragments to produce a second plurality of circularized nucleicacid sequences, wherein the one or more second adapters form a secondlinker between the 5′end and the 3′end of the second circularizednucleic acid sequence fragments, and wherein the second linker comprisestwo priming sites, f) amplifying the nucleic acid sequence fragmentsusing two different primers that are complementary to the priming sitesin the second linker, and g) characterizing the paired tags, therebycharacterizing the nucleic acid sequence.

In one embodiment, provided herein is a composition comprising nucleicacid sequence elements arranged in the following order:

-   -   linker 1--5′end tag--linker 2--3′end tag--linker 3        wherein the 5′end tag and the 3′end tag comprise a paired tag        derived from a single contiguous nucleic acid sequence fragment.        In a particular embodiment, linker 2 comprises at least two        restriction endonuclease recognition sites specific for a        restriction endonuclease that cleaves the nucleic acid sequence        fragment distally to the restriction endonuclease recognition        site, and is oriented in such a way that one of the sites        directs cleavage within the 5′end tag or at the junction of        linker 1 and the 5′end tag, and the other site directs cleavage        within the 3′ end tag or at the junction of linker 3 and the        3′end tag. In another embodiment, the linker 2 comprises at        least two restriction endonuclease recognition sites specific        for a restriction endonuclease that cleaves the nucleic acid        sequence fragment distally to the restriction endonuclease        recognition site, and is oriented in such a way that one of the        sites directs cleavage within the 5′end tag or at the junction        of linker 1 and the 5′end tag, and the other site directs        cleavage within the 3′ end tag or at the junction of linker 3        and the 3′end tag, and at least one recognition site for a        rare-cutting restriction endonuclease located between the two        restriction endonuclease recognition sites specific for a        restriction endonuclease that cleaves the nucleic acid sequence        fragment distally to the restriction endonuclease recognition        site. In one example, linker 1 and linker 3 are the same        sequence in reverse orientation. In a further embodiment,        oligonucleotides complementary to sequences present in linker 1        and linker 3 are used for amplification. In another example,        linker 1 and linker 3 are derived by cleavage of a circular        nucleic acid molecule with a rare-cutting restriction        endonuclease comprising a recognition site between linker 1 and        linker 3.

In a further embodiment of the invention, provided herein is acomposition comprising a circular nucleic acid molecule, whereinsequence elements are arranged in the following circular order:

wherein the 5′end tag and the 3′end tag comprise a paired tag derivedfrom a single contiguous nucleic acid sequence fragment. In oneembodiment, linker 1 comprises at least two restriction endonucleaserecognition sites specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site, and are oriented in such a way that oneof the sites directs cleavage within the 5′end tag or at the junction ofthe 5′end tag and linker 2, and the other site directs cleavage withinthe 3′ end tag or at the junction of the 3′end tag and linker 2. Ianother embodiment, linker 2 comprises at least two restrictionendonuclease recognition sites specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and are oriented in such away that one of the sites directs cleavage within the 5′end tag or atthe junction of the 5′end tag and linker 2 and, and the other sitedirects cleavage within the 3′ end tag or at the junction of the 3′endtag and linker 2, and at least one recognition site for a rare-cuttingrestriction endonuclease located between the two restrictionendonuclease recognition sites specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site. In one embodiment, linker 2is palindromic. In another embodiment, linker 2 comprises a recognitionsite for a rare-cutting restriction endonuclease. In a furtherembodiment, oligonucleotide primers complementary to sequences in eitherlinker 1 or linker 2, or in both linker 1 and linker 2 are used forisothermic amplification, for example, oligonucleotide primerscomplementary to sequences in either linker 1 or linker 2, and orientedin opposite directions such that a linear nucleic acid fragment isproduced that preserves the orientation of the 5′end tag and the 3′endtag with respect to each other are used.

In a further aspect of the invention, provided herein is a method forcharacterizing a nucleic acid sequence comprising the steps of a)fragmenting a nucleic acid sequence to produce a plurality of nucleicacid sequence fragments having a 5′ end and a 3′ end, b) joining one ormore first adapters to the 5′ and 3′ ends, wherein the one or more firstadapters are compatible for promoting intramolecular ligation, therebyproducing a first plurality of modified nucleic acid sequence fragments,intramolecularly ligating the first plurality of modified nucleic acidsequence fragments thereby producing a first plurality of circularizednucleic acid sequences, wherein the one or more first adapters forms afirst linker between the 5′end and the 3′end of the circularized nucleicacid sequence fragment, and wherein the first linker comprises asequence or chemical moiety that enables affinity capture, c)fragmenting the first plurality of circularized nucleic acid sequencesby random shearing or by other means, thereby producing first linearfragments comprising the first linker and a paired tag comprising the 5′end and a 3′ end of the nucleic acid sequence fragment, d) purifying thelinear fragments by affinity capture, e) joining one or more secondadapters to the each of the 5′ and 3′ ends of the first linearfragments, wherein the one or more second adapters are compatible forpromoting intramolecular ligation, thereby producing a second pluralityof modified nucleic acid sequence fragments, and intramolecularlyligating the second plurality of modified nucleic acid sequencefragments to produce a second plurality of circularized nucleic acidsequences, wherein the on or more second adapters form a second linkerbetween the 5′end and the 3′end of the second circularized nucleic acidsequence fragments, and wherein the second linker comprises two primingsites separated by a rare-cutting restriction endonuclease cleavagesite, f) cleaving the second plurality of circularized nucleic acidsequences using a rare-cutting restriction endonuclease that recognizesthe cleavage site in the second adapter, thereby producing a secondplurality of linear fragments, g) amplifying the second plurality oflinear fragments using two different primers that are complementary tothe priming sites in the second linker, h) characterizing the pairedtags, thereby characterizing the nucleic acid sequence.

In a further aspect of the invention, a method for identifying nucleicacid sequences that encode at least two interacting proteins isprovided, comprising the steps of a) combining (i) a first vectorcomprising (1) a nucleic acid sequence that encodes a first protein thatinteracts with a second protein, and (2) a first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and (ii) a second vectorcomprising (1) a nucleic acid sequence that encodes the second protein;and (2) a second restriction endonuclease recognition site specific fora restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site,thereby producing a combination, b) optionally maintaining thecombination under conditions in which the first protein and the secondprotein are expressed and interact, c) joining the first vector with thesecond vector, thereby forming a contiguous nucleic acid sequence thatcomprises (i) the nucleic acid sequence that encodes a first proteinthat interacts with a second protein, (ii) the first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, (iii) the nucleic acidsequence that encodes the second protein, and (iv) the secondrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, d) cleaving the firstrestriction endonuclease recognition site and the second restrictionendonuclease recognition site in the contiguous nucleic acid sequencewith restriction endonucleases that cleave the contiguous nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a 5′ end tag and a 3′ end tag of the contiguousnucleic acid sequence, e) joining the 5′ end tag to the 3′ end tag,thereby producing a paired tag, and f) sequencing the paired tag,thereby identifying nucleic acid sequences that encode at least twointeracting proteins.

In an additional embodiment of the invention, provided is a method foridentifying nucleic acid sequences that encode at least two interactingproteins comprising the steps of a) combining (i) a first vectorcomprising (1) a nucleic acid sequence that encodes a first protein thatinteracts with a second protein, and (2) a first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and (ii) a second vectorcomprising (1) a nucleic acid sequence that encodes the second protein,and (2) a second restriction endonuclease recognition site specific fora restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site,thereby producing a combination, b) optionally maintaining thecombination under conditions in which the first protein and the secondprotein are expressed and interact, c) joining the first vector with thesecond vector, thereby forming a contiguous nucleic acid sequence thatcomprises (i) the nucleic acid sequence that encodes a first proteinthat interacts with a second protein, (ii) the first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, (iii) the nucleic acidsequence that encodes the second protein, and (iv) the secondrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, d) sequencing thecontiguous nucleic acid sequence, thereby identifying nucleic acidsequences that encode at least two interacting proteins.

In another embodiment of the invention, provided is a method foridentifying nucleic acid sequences that encode at least two interactingproteins comprising the steps of a) combining, (i) a first vectorcomprising (1) a nucleic acid sequence that encodes a first protein thatinteracts with a second protein, and (2) a first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and (ii) second vectorcomprising (1) a nucleic acid sequence that encodes the second protein;and (2) a second restriction endonuclease recognition site specific fora restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site,thereby producing a combination, b) optionally maintaining thecombination under conditions in which the first protein and the secondprotein are expressed and interact, c) joining the first vector with thesecond vector, thereby forming a contiguous nucleic acid sequence thatcomprises (i) the nucleic acid sequence that encodes a first proteinthat interacts with a second protein, (ii) the first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, (iii) the nucleic acidsequence that encodes the second protein, and (iv) the secondrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, d) cleaving the firstrestriction endonuclease recognition site and the second restrictionendonuclease recognition site in the contiguous nucleic acid sequencewith restriction endonucleases that cleave the contiguous nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a paired tag comprising a 5′ end tag and a 3′ end tagof the contiguous nucleic acid sequence, e) sequencing the paired tag,thereby identifying nucleic acid sequences that encode at least twointeracting proteins.

In a further embodiment of the invention, provided is a method foridentifying a plurality of nucleic acid sequences that encode at leasttwo interacting proteins comprising the steps of a) combining (i) aplurality of first vectors each comprising (1) a nucleic acid sequencethat encodes a first protein that interact with a second protein; and(2) a first restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site, and (ii) aplurality of second vectors each comprising (1) a nucleic acid sequencethat encodes the second protein; and (2) a second restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, thereby producing acombination comprising a plurality of first vectors and a plurality ofsecond vectors, b) optionally maintaining the combination underconditions in which the plurality of first vectors encoding a firstprotein and the plurality of second vectors encoding a second proteinare expressed and the first protein and second protein interact, c)joining the first vectors with the second vectors, wherein the firstvectors and second vectors encode interacting proteins, thereby forminga plurality of contiguous nucleic acid sequences that each comprise (i)the nucleic acid sequence that encodes a first protein that interactswith a second protein, (ii) the first restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site, (iii) the nucleic acid sequence thatencodes the second protein, and (iv) the second restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site, d) cleaving the first restrictionendonuclease recognition site and the second restriction endonucleaserecognition site in each contiguous nucleic acid sequence withrestriction endonucleases that cleave the contiguous nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a plurality of paired tags comprising a 5′ end tag anda 3′ end tag of the contiguous nucleic acid sequence, e) joining thepaired tags; and f) sequencing the joined paired tags, therebyidentifying a plurality of nucleic acid sequences that encode at leasttwo interacting proteins.

In a further embodiment of the invention, a method for identifyingnucleic acid sequences that encode at least two interacting proteins isprovided, comprising the steps of a) combining (i) a first vectorcomprising (1) a nucleic acid sequence that encodes a first protein thatinteracts with a second protein, (2) a first restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site; and (3) a second restriction endonucleaserecognition site, and (ii) a second vector comprising (1) a nucleic acidsequence that encodes the second protein, (2) a third restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and (3) a fourth restrictionendonuclease recognition site, thereby producing a combination, b)optionally maintaining the combination under conditions in which thefirst protein and the second protein are expressed and interact, c)joining the first vector with the second vector, thereby forming acontiguous nucleic acid sequence that comprises (i) the nucleic acidsequence that encodes a first protein that interacts with a secondprotein, (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, (iii) the second restriction endonuclease recognition site, (iv)the nucleic acid sequence that encodes the second protein, (v) the thirdrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, and (vi) the fourthrestriction endonuclease recognition site, d) cleaving the secondrestriction endonuclease recognition site and the fourth restrictionendonuclease recognition site in the contiguous nucleic acid sequencewith restriction endonucleases thereby producing compatible ends in thecontiguous nucleic acid sequence, e) maintaining the contiguous nucleicacid sequence under conditions in which the compatible ends in thecontiguous nucleic acid sequence intramolecularly ligate, therebyproducing a circularized nucleic acid sequence, and f) sequencing thecircularized nucleic acid sequence, thereby identifying nucleic acidsequences that encode at least two interacting proteins. In a particularembodiment, the cleaving of the second restriction endonucleaserecognition site and the cleaving of the fourth restriction endonucleaserecognition site in the contiguous nucleic acid sequence releases afragment containing a recombined site-specific recombinase recognitionsite between the nucleic acid sequence that encodes a sequence from thefirst protein and a sequence from the second protein that interact witheach other.

In another aspect of the invention, provided is a method for identifyingnucleic acid sequences that encode at least two interacting proteinscomprising the steps of a) combining (i) a first vector comprising (1) anucleic acid sequence that encodes a first protein that interacts with asecond protein, (2) a first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, and (3) a second restriction endonuclease recognition site, and(ii) a second vector comprising, (1) a nucleic acid sequence thatencodes the second protein, (2) a third restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site, and (3) a fourth restriction endonucleaserecognition site, thereby producing a combination, b) optionallymaintaining the combination under conditions in which the first proteinand the second protein are expressed and interact, c) joining the firstvector with the second vector, thereby forming a contiguous nucleic acidsequence that comprises (i) the nucleic acid sequence that encodes afirst protein that interacts with a second protein, (ii) the firstrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, (iii) the secondrestriction endonuclease recognition site; (iv) the nucleic acidsequence that encodes the second protein, and (v) the third restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, (vi) a fourth restrictionendonuclease recognition site, d) cleaving the second restrictionendonuclease recognition site and the fourth restriction endonucleaserecognition site in the contiguous nucleic acid sequence withrestriction endonucleases, thereby producing compatible ends in thecontiguous nucleic acid sequence, e) maintaining the contiguous nucleicacid sequence under conditions in which the compatible ends in thecontiguous nucleic acid sequence intramolecularly ligate, therebyproducing a circularized nucleic acid sequence, f) cleaving the firstrestriction endonuclease recognition site and the third restrictionendonuclease recognition site in the circularized nucleic acid sequencewith restriction endonucleases that cleave the circularized nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a paired tag comprising a 5′ end tag and a 3′ end tagof the circularized nucleic acid sequence, and g) sequencing the pairedtag, thereby identifying nucleic acid sequences that encode at least twointeracting proteins.

In a further embodiment of the invention, provided is a method foridentifying a plurality of nucleic acid sequences that encode at leasttwo interacting proteins comprising the steps of a) combining (i) aplurality of first vectors each comprising (1) a nucleic acid sequencethat encodes a first protein that interacts with a second protein,

-   -   (2) a first restriction endonuclease recognition site specific        for a restriction endonuclease that cleaves the nucleic acid        sequence fragment distally to the restriction endonuclease        recognition site, and (3) a second restriction endonuclease        recognition site, and (ii) a plurality of second vector each        comprising (1) a nucleic acid sequence that encodes the second        protein, (2) a third restriction endonuclease recognition site        specific for a restriction endonuclease that cleaves the nucleic        acid sequence fragment distally to the restriction endonuclease        recognition site, and (3) a fourth restriction endonuclease        recognition, thereby producing a combination comprising a        plurality of first vectors and a plurality of second vectors, b)        maintaining the combination under conditions in which the        plurality of first vectors encoding a first protein and the        plurality of second vectors encoding a second protein are        expressed and the first protein and second protein interact c)        selecting the combinations of a first vector that encodes a        first protein and a second vector that encodes a second protein,        wherein the first protein interacts with the second protein, d)        joining the first vectors with the second vectors, wherein the        first vectors and second vectors encode interacting proteins,        thereby forming a plurality of contiguous nucleic acid sequences        that each comprise (i) the nucleic acid sequence that encodes a        first protein that interacts with a second protein, (ii) the        first restriction endonuclease recognition site specific for a        restriction endonuclease that cleaves the nucleic acid sequence        fragment distally to the restriction endonuclease recognition        site, (iii) the second restriction endonuclease recognition site        adjacent to the first restriction endonuclease site, (iv) the        nucleic acid sequence that encodes the second protein, (v) the        third restriction endonuclease recognition site specific for a        restriction endonuclease that cleaves the nucleic acid sequence        fragment distally to the restriction endonuclease recognition        site, and (vi) the fourth restriction endonuclease recognition        site, d) cleaving the second restriction endonuclease        recognition site and the fourth restriction endonuclease        recognition site in the contiguous nucleic acid sequence with        restriction endonucleases that leave compatible ends, e)        maintaining the contiguous nucleic acid sequence under        conditions in which the compatible ends intramolecularly ligate,        thereby producing a circularized nucleic acid sequence that        encodes a sequence from the first protein and a sequence from        the second protein that interact with each other, f) cleaving        the first restriction endonuclease recognition site and the        third restriction endonuclease recognition site in each        circularized nucleic acid sequence with restriction        endonucleases that cleave each circularized nucleic acid        sequence distally to the restriction endonuclease recognition        sites, thereby producing a plurality of paired tags comprising a        5′ end tag and a 3′ end tag of the circularized nucleic acid        sequence, g) joining the paired tags, and h) sequencing the        joined paired tags, thereby identifying a plurality of nucleic        acid sequences that encode at least two interacting proteins.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a graph depicting the effect of clone size and distribution.

FIG. 2 is a graph depicting the number of segmental duplicationsidentified in the rat genome versus the percent identity of the cognatepairs.

FIG. 3 is a schematic of sequence assembly (derived from Holt et al.,Science 298:129-149 (2002)).

FIG. 4 is a schematic of paired tags in a concatemer.

FIG. 5 is an outline of the paired tag, two-hybrid method.

FIG. 6A-D are schematics outlining an example of a paired tag protocol.FIG. 6A is a schematic outlining the vector, and the steps of excising astuffer fragment and preparation of inserts. FIG. 6B is a schematicoutlining the steps of cloning of the inserts, optional exonucleasetreatment, restriction endonuclease digestion with MmeI, and ligation toa degenerate linker. FIG. 6C is a schematic outlining the steps of PCRamplification, excising of paired tags, concatenation of paired tags andcloning of paired tags into a suitable vector, such as a sequencingvector. FIG. 6D is a list of particular nucleic acid sequences of theinvention.

FIG. 7 is a schematic of one embodiment of paired tag formation.

FIG. 8 is a schematic of one embodiment of paired tag formation.

FIG. 9 is a schematic of one embodiment for generating paired genomesequence tags.

FIG. 10 is a schematic of one embodiment for generating paired genomesequence tags.

FIG. 11 is a schematic of an affinity tag with two unique primersequences.

FIG. 12 is a schematic of one embodiment for generating paired genomesequence tags.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for producing a paired tag froma nucleic acid sequence (also referred to herein as a nucleotidesequence). In one embodiment, the nucleic acid sequence (e.g. DNA, RNA)comprises at least two restriction endonuclease recognition sitesspecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite. In another embodiment, the nucleic acid sequence comprises atleast one restriction endonuclease recognition site specific for arestriction endonuclease that cleaves both upstream and downstream fromthe recognition site. The restriction endonuclease recognition sitespresent in the nucleic acid sequence can be the same or different. Inaddition, the restriction endonuclease recognition sites present in thenucleic acid sequence can be cleaved by the same or differentrestriction endonucleases.

The present invention also provides a method for producing a paired tagfrom a nucleic acid sequence, wherein the nucleic acid sequencecomprises at least one recombination site, wherein a recombination eventat this recombination site in the nucleic acid sequence produces apaired tag from the nucleic acid sequence.

As used herein, a “paired tag” is produced from a nucleic acid sequenceand comprises a 5′ end of a nucleic acid sequence (e.g., a contiguousnucleic acid sequence) paired or joined with the 3′ end of the samenucleic acid sequence, wherein a portion of the internal sequence of thecontiguous nucleic acid sequence is removed. In one embodiment, a pairedtag can be represented as:

wherein “5′------” represents a 5′ end tag, “------3′” represents a 3′end tag, and “▪” represents a linker (or adapter) that links the 5′ endtag to the 3′ end tag. Alternatively, a paired tag can be representedas:

wherein “------5′” represents a 5′ end tag, “3′------” represents a 3′end tag, and “▪” represents an adapter (or linker). As will berecognized by the person of skill in the art, the orientation of the 5′end tag and 3′ end tag can be reversed. As discussed below, the linkeror adapter can comprise: at least one endonuclease recognition site,(e.g., for a restriction endonuclease enzyme such as a rare cuttingenzyme, an enzyme that cleaves distally to its recognition sequence); anoverhang that is compatible with joining to a complementary overhangfrom a restriction endonuclease digestion product; an attachment capturemoiety, such as biotin; primer sites (for use in, e.g., amplification,RNA polymerase reactions); Kozak sequence, promoter sequence, (e.g. T7or SP6); and/or an identifying moiety, such as a fluorescent label.

A paired tag is distinguished from a ditag since a ditag is a randomizedpairing of two tags usually from more than one nucleic acid sequence,for example, a 5′ end of sequence A and the 3′ end of sequence B. Incontrast, a paired tag as described herein, is not a randomized pairingof two tags, but the pairing of two tags that are produced from a singlecontiguous nucleic acid sequence.

Paired tags facilitate the assembly (such as whole genome assembly, orgenome mapping) of a nucleic acid sequence, such as a genomic DNAsequence, even if either tag (for example, the 5′ tag) is generated froma non-informative sequence (for example, a repeat sequence) and theother tag in the pair (for example, the 3′ tag) is generated from aninformative sequence based on the paired tag's “signature”. A pairedtag's signature is derived from the size of the original nucleic acidsequence from which the paired tag represents the 5′ end and 3‘end ofthe paired tag’s nucleic acid sequence. The random association of tagsto form ditags does not retain any signature as the two tags in theditag generally do not represent the 5′ end and 3′ end of any contiguousnucleic acid sequence. In addition, a paired tag can identify thepresence of an inverted nucleic acid sequence in, for example, a genomicDNA sample, because of the paired tag's signature. Randomly associatedtags that form ditags cannot detect the presence of an inverted nucleicacid sequence because the ditag does not retain a signature. Forexample, a database version of one genome places tags in the order of:X-Y-Z-A in a contiguous sequence. Paired tags from this sequencesgenerates the following two paired tags: X-Y and Z-A. In a comparisongenome, for example, from a cancer cell, the paired tags from the samecontiguous sequence generates the following two paired tags: X-Z andY-A. These two paired tags indicates the order of the tags in thecontiguous sequence of the cancer cell genome as: X-Z-Y-A. Thus, it isdetermined that the fragment Y-Z is inverted. Ditags will not havesufficient information to determine if a contiguous sequence has aninversion due to the random association of any two tags together.

A contiguous nucleic acid sequence is a nucleic acid sequence having asequential sequence of nucleic acids, for example, deoxyribonucleicacids, ribonucleic acids, derivatives or analogs thereof, andcombinations thereof, as will be understood by one of skill in the art.

In one embodiment, a “contiguous nucleic acid sequence” is a nucleicacid fragment. Such a nucleic acid fragment can be obtained, forexample, from sheared DNA, such as genomic DNA, from enzyme-digestedDNA, for example, restriction enzyme-digested or non-specificendonuclease-digested DNA, or a combination thereof, or from a modifiedgenomic DNA fragment derived by treatment of genomic DNA, for example,with one or more nucleic acid modifying enzymes. In a furtherembodiment, the contiguous nucleic acid sequence comprises at least twonucleic acid sequences that encode at least two interacting proteins,wherein the at least two nucleic acid sequences have been joined to forma contiguous nucleic acid sequence.

A “5′end tag” (also referred to as a “5′tag”) and a “3′end tag” (alsoreferred to as a “3′tag”) of a contiguous nucleic acid sequence can beshort nucleic acid sequences, for example, the 5′ end tag or 3′ end tagcan be from about 6 to about 80 nucleotides, from about 6 to about 600nucleotides, from about 6 to about 1200 nucleotides or longer, fromabout 10 to about 80 nucleotides, from about 10 to about 1200nucleotides, from about 10 to about 1500 nucleotides or longer in lengththat are from the 5′ end and 3′ end, respectively, of the contiguousnucleic acid sequence. In one embodiment, the 5′ end tag and/or the 3′end tag are about 14 nucleotides, about 20 nucleotides or about 27nucleotides. The 5′ end tag and a 3′ end tag are generally sufficient inlength to identify the contiguous nucleic acid sequence from which theywere produced. In one embodiment, the 5′ end tag and/or the 3′ end tagare produced after cleavage of the contiguous nucleic acid sequence witha restriction endonuclease having a recognition site located at the 5′and/or 3′ end of the contiguous nucleic acid sequence. In a particularembodiment, the restriction endonuclease cleaves the contiguous nucleicacid sequence distally to (outside of) its restriction endonucleaserecognition site. The 5′end tag and/or 3′end tag can also be producedafter cleavage by other fragmentation means, such as random shearing,treatment with non-specific endonucleases or other fragmentation methodsas will be understood by one skilled in the art. In some embodiments,cleavage can occur in a linker or adapter sequence, in otherembodiments, cleavage can occur outside a linker or adapter sequence,such as in a genomic DNA fragment.

Traditional classification of restriction endonucleases (restrictionenzymes) generally divide restriction endonucleases according to theirsubunit composition, cleavage position, sequence-specificity andco-factor requirements. For example, restriction endonucleases can beclassified as type I, type II, type IIs, typeIIB, type III or type IVrestriction endonucleases. Restriction endonucleases are alsocharacterized according to their cleavage frequency for a particularsequence, such as a genomic sequence. For example, a restrictionendonuclease can be characterized as a “rare-cutting restrictionendonuclease” or a “rare-cutting restriction enzyme” based on the rarityor infrequency of its recognition site in a nucleic acid sequence, e.g.,a genomic sequence. Examples of rare-cutting restriction endonucleasesare well known to those of skill in the art, and include, for example,AsiSI, NotI. Further examples of enzymes that are rare-cutting includehoming endonucleases. Homing endonucleases are rare-cutting enzymesencoded by introns and inteins (Belfort M. and Roberts R. J., NucleicAcids Res. 25:3379-88 (1997)). Examples of homing endonucleases includeI-CeuI, I-SceI, PI-PspI and PI-SceI.

In one embodiment, the restriction endonuclease for use in the methodsof the invention includes one or more restriction endonucleases thatcleave a nucleic acid distally to its restriction endonucleaserecognition site. As used herein, “restriction endonucleases that cleavea nucleic acid distally to its restriction endonuclease recognitionsite” refers to a restriction endonuclease that recognizes a particularsite within a nucleic acid sequence and cleaves this nucleic acidsequence outside the region of the recognition site (cleavage occurs ata site which is distal or outside the site recognized by the restrictionendonuclease). In one embodiment, a restriction endonuclease thatcleaves a nucleic acid distally to its restriction endonucleaserecognition site cleaves on one side of the restriction endonucleaserecognition site (for example, upstream or downstream of the recognitionsite). In another embodiment, restriction endonuclease that cleaves anucleic acid distally to its restriction endonuclease recognition sitecleaves on both sides of the restriction endonuclease recognition site(for example, upstream and downstream of the recognition site). Inanother embodiment, the restriction endonuclease cleaves once betweentwo restriction endonuclease recognition sites. Examples of suchrestriction endonucleases are well known in the art, and includerestriction endonucleases classified as Type I (e.g., CfrA I, Eco377 I,Hind I, KpnA, IngoAV, StySK I), Type Ius (e.g., Mmel, Fok I, Bsg I, BpmI, Mbo II, and Alw I), Type IIB (e.g. AlfI, AloI, BaeI, BcgI, BplI,BsaXI, BslFI, Bsp24I, CjeI, CjePI, CspCI, Fall, HaeIV, Hin4I, PpiI, andPsrI), Type III (e.g., EcoP I, EcoP15I, Hine I, Hinf III) and Type IV(e.g., Eco57 I, Bcg I [recently re-classified as a Type IIB], BseMII)restriction endonucleases.

The present invention provides in one embodiment, a method for producinga paired tag from a nucleic acid sequence. In one embodiment, thenucleic acid sequence comprises at least one restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence distally to the restriction endonucleaserecognition site. In another embodiment, the nucleic acid sequencecomprises two restriction endonuclease recognition sites specific for arestriction endonuclease that cleaves the nucleic acid sequence distallyto the restriction endonuclease recognition site. In a particularembodiment, the restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence distallyto the recognition site is adjacent to the nucleic acid sequence ofinterest. These restriction endonuclease recognition sites are cleavedusing the restriction endonuclease that is specific for the restrictionendonuclease recognition sites. As a result of this cleavage, a 5′ endtag and a 3′ end tag is produced from the nucleic acid sequence. The 5′end tag is joined with the 3′ end tag of the nucleic acid sequence toproduce a paired tag from the nucleic acid sequence. The two restrictionendonuclease recognition sites specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site can be the same or different.

In another embodiment, the invention provides a method for generatingpaired tags from the 5′ and 3′ ends of a set of genomic DNA fragments,wherein the tags are generated by fragmentation means other than bycleavage with restriction endonucleases that cleave distally to theirrecognition sites, for example, by random shearing or by othernon-specific cleavage methods. This is achieved, for example, byperforming two rounds of intramolecular ligation in which a linker isincorporated between the 5′ and 3′ ends of the genomic DNA fragments,with a fragmentation step performed between the first and secondintramolecular ligation steps. This method produces 5′ and 3′ end tagsof the genomic DNA fragment that can be long in length, therebyfacilitating long sequence read lengths.

As used herein, “joining” refers to methods such as ligation, annealingor recombination used to adhere one component to another. Recombinationcan be achieved by any methods known in the art. For example,recombination can be a Cre/Lox recombination. In one embodiment, therecombination is a between a lox71 site and a lox66 site. In anotherembodiment, joining of a nucleic acid sequence to another nucleic acidsequence is performed by intermolecular ligation. For example, twonucleic acid sequences can be joined to form one contiguous nucleic acidsequence. A typical example of intermolecular ligation is cloning anucleic acid sequence into a vector. A vector is generally understood inthe art, and is understood to contain an origin of replication (“ori”).In another embodiment, intermolecular ligation can be achieved using anon-vector vehicle (also referred to herein as “without cloning”).Without cloning means that a joining of nucleic acid sequence is not anaccomplished using vector is not used to clone into. For example, a DNAsequence or an oligonucleotide, such as a linker or an adapter can beintermolecularly ligated to the nucleic acid sequence of interest tofacilitate joining of nucleic acid sequences.

In one embodiment, intermolecular ligation is between two nucleic acidsequences having sticky ends (“sticky ends ligation”). In an alternativeembodiment, intermolecular ligation is between two nucleic acidsequences having blunt ends (“blunt end ligation”). In another example,intermolecular ligation is between a number of paired tags, for example,to form a concatemer. In a further embodiment, intermolecular ligationis between at least three components, such as two paired tags and alinker, or two tags and a linker. The linker functions to link twocomponents together, for example, the linking of one or more paired tagstogether. As used herein, a “linker” is a nucleic acid fragment, such asDNA, as is understood in the art. The linker can be double-stranded orsingle-stranded. In general, the linker acts to link two componentstogether, such as linking the 5′ end of a nucleic acid sequence to the3′ end of a nucleic acid sequence. Furthermore, a linker can comprise:at least one endonuclease recognition site, (e.g., for a restrictionendonuclease enzyme such as a rare cutting enzyme, an enzyme thatcleaves distally to its recognition sequence); an overhang that iscompatible with joining to a complementary overhang from a restrictionendonuclease digestion product; an attachment moiety, such as biotin;primer sites, for use in, (e.g., amplification, RNA polymerasereactions; Kozak sequence, promoter sequence), (e.g. T7 or SP6; and/oran identifying moiety, such as a fluorescent label). A double-strandedlinker can be produced by annealing two oligonucleotides, for example,and typically ranges between about 6 to about 1000 base pairs in length,but more typically is between about 30 and about 100 base pairs inlength. In one embodiment, the linker provides a link between twocomponents having non-complementary ends. In another embodiment, thelinker is a degenerate linker. As used herein, a “degenerate linker” isa linker having in at least one position, a plurality of possiblenucleotides, as will be understood by those of skill in the art. In aparticular embodiment, the linker has the sequence NNATGATGNN (SEQ IDNO: 1), where N=any nucleotide. In another embodiment, the linkercomprises a restriction endonuclease recognition site. In a particularembodiment, the linker comprises a rare cutting restriction endonucleaserecognition site. For example, the linker having SEQ ID NO: 1 allows the3′ overhangs of paired tags to come together when the paired tagproduces a sequence comprising “linker-5′ TAG-3′TAG-linker”. In anotherexample, the linker and the paired tag produces a sequence comprising“5′ TAG-linker-3′ TAG”. Other examples are those that generate thearrangement “linker-5′ TAG-linker-3′ TAG-linker”. As will be recognizedby one of skill in the art, any of the linker moieties can be replacedby a vector.

In another embodiment, joining of two nucleic acid sequences isperformed by intramolecular ligation. Intramolecular ligation includes,for example, the ligation of the 5′ end of a nucleic acid sequencefragment to the 3′ end of the same nucleic acid sequence fragment. Inone embodiment, intramolecular ligation produces a circular nucleic acidsequence. For example, in one embodiment, joining of a 5′ end tag to the3′ end tag of a contiguous sequence is performed by intramolecularligation. In a further embodiment, joining of a 5′ end tag to the 3′ endtag of a contiguous sequence is performed by intramolecular ligation,wherein the 5′ end tag nucleic acid sequence and the 3′ end tag nucleicacid sequence have, for example, sticky ends (“sticky ends ligation”).In another embodiment, joining of a 5′ t end tag to the 3′ end tagcomprised in a contiguous sequence is performed by intramolecularligation, wherein the 5′ end tag nucleic acid sequence and the 3′ endtag nucleic acid sequence have, for example, blunt ends (“blunt endligation”).

In one embodiment, intramolecular ligation is performed by ligation of anucleic acid sequence fragment in the presence of a linker such that oneend of the linker is first ligated to one end of the nucleic acidsequence fragment by intermolecular ligation, then the other end of thelinker is ligated to the other end of the nucleic acid sequence fragmentby intramolecular ligation. This results in a circular molecule in whichthe linker is inserted between the two ends of the nucleic acid sequencefragment. Typically, the ends of the linker and the nucleic acidsequence fragment are complementary to each other, but not to themselvesto avoid self-ligation of the inserts and linkers.

In the method of the invention, conditions that favor intramolecularligation over intermolecular ligation are used when attempting tocircularize DNA molecules in order to avoid chimeric ligation (i.e., theligation of 5′ and 3′ ends from two different DNA molecules whichresults in the production of ditags). Conditions that favorintramolecular ligation over intermolecular ligation are known in theart. In one embodiment, intramolecular ligation is favored overintermolecular ligation by performing ligation at low DNAconcentrations, and also in the presence of crowding reagents likepolyethylene glycol (PEG) at low salt concentrations (Pfeiffer andZimmerman, Nucl. Acids Res. (1983) 11(22): 7853-7871). Ligation at lowDNA concentration can be expensive and impractical since large reactionvolumes are used at high ligase concentration but dilute DNAconcentration. The use of PEG increases the reaction rate, therefore,long reaction times can still result in intermolecular products. Inaddition, volume exclusion does not eliminate diffusion of DNA moleculessuch that given enough time, DNA molecules will diffuse within reach ofone another and ligate to one another. To overcome these problems,water-in-oil emulsions can be used. Water-in-oil emulsions have beendescribed by Dressman et al. for single molecule PCR (Dressman et al.,PNAS (2003), 100(15): 8817-8822). By creating a water-in-oil emulsion,billions of micro-reaction bubbles, for example, 10 micrometers indiameter, can be generated. Using a dilute enough DNA concentration canensure that only one or less than one molecule of DNA exists in anygiven micro-reactor. Under such conditions, long reaction times andadditives (such as PEG, MgCl₂, DMSO) which increase the reaction rate ofligase (Alexander et al., Nuc. Acids Res. (2003) 31(12): 3208-3216) canbe utilized without any risk of intermolecular ligation.

In one embodiment, emulsion ligation of a nucleic acid sequence fragmentis performed in the presence of a linker or adapter, such that thelinker or adapter is incorporated into the resulting circular moleculesbetween the 5′ and 3′ ends of the nucleic acid sequence fragment. Inanother embodiment, emulsion ligation of a nucleic acid sequencefragment is performed in the presence of a substrate, for example, amagnetic bead coupled to a linker or adaptor, such that the resultingcircularized DNA becomes immobilized (covalently or non-covalently) ontothe substrate. In each of these embodiments, the concentration ofnucleic acid sequence fragments, linkers, and beads can be modulatedindependently to maximize intramolecular ligation or, if relevant,immobilization of an individual nucleic acid sequence fragment onto asingle bead.

In another embodiment, emulsion ligation of a nucleic acid sequencefragment is performed in the presence of a substrate, for example, amagnetic bead coupled to a linker or adaptor, such that the resultingcircularized DNA becomes immobilized onto the substrate. In each ofthese embodiments, the concentration of nucleic acid sequence fragments,linkers, and beads can be modulated independently to maximizeintramolecular ligation or, if relevant, immobilization of an individualnucleic acid sequence fragment onto a single bead. As used herein,“immobilized” means attached to a surface by covalent or non-covalentattachment means, as understood in the art. As used herein, a“substrate” is a solid or polymeric support such as a silicon or glasssurface, a magnetic bead, a semisolid bead, a gel, or a polymericcoating applied to the another material, as is understood in the art.

Circularized nucleic acid molecules produced by intramolecular ligationwith an intervening linker may be purified by a variety of methods knownin the art, such as by gel electrophoresis, by treatment with anexonuclease (e.g., Bal31 or “plasmid-safe” DNase) to removecontaminating linear molecules. Nucleic acid molecules incorporating alinker between the 5′ and 3′ ends of the starting nucleic acid sequencefragment can be purified by affinity capture using a number of methodsknown in the art, such as the use of a DNA binding protein that binds tothe linker specifically, by triplex hybridization using a nucleic acidsequence complementary to the linker, or by means of a biotin moietycovalently attached to the linker. Affinity capture methods typicallyinvolve the use of capture reagents attached to a substrate such as asolid surface, magnetic bead, or semisolid bead or resin.

A nucleic acid sequence, fragment, or paired tag having compatible endsare understood by one of skill in the art to mean that the ends arecompatible with joining to another nucleic acid sequence, fragment orpaired tag as provided herein. Compatible ends can be “sticky ends”having a 5′ and/or 3′ overhang, or alternatively, compatible ends can be“blunt ends” having no 5′ and/or 3′ overhang. Sticky ends permitsequence-dependent ligation, whereas blunt ends permitsequence-independent ligation. Compatible ends are produced by any knownmethods that are standard in the art. For example, compatible ends of anucleic acid sequence are produced by restriction endonuclease digestionof the 5′ and/or 3′ end. In another embodiment, compatible ends of anucleic acid sequence are produced by introducing (for example, byannealing, ligating, or recombination) an adapter to the 5′ end and/or3′ end of the nucleic acid sequence, wherein the adapter comprises acompatible end, or alternatively, the adapter comprises a recognitionsite for a restriction endonuclease that produces a compatible end oncleavage. As used herein, an “adapter” is, for example, nucleic acidfragment, such as DNA (double stranded, single stranded), as will beunderstood by one of skill in the art. An adapter can be used to modifythe 5′ end and/or the 3′ end of a nucleic acid sequence. In oneembodiment, the adapter can comprise: at least one endonucleaserecognition site, e.g., for a restriction endonuclease enzyme such as arare cutting enzyme, an enzyme that cleaves distally to its recognitionsequence; an overhang that is compatible with joining to a complementaryoverhang from a restriction endonuclease digestion product; anattachment moiety, such as biotin; and/or an identifying moiety, such asa fluorescent label. Such adapters can be produced, for example, byannealing a pair of oligonucleotides having the appropriate nucleic acidsequences. In another embodiment, compatible ends of a nucleic acidsequence are produced by introducing (for example, by annealing,ligating, or recombination) the nucleic acid sequence into a vector. Inone embodiment, the nucleic acid sequence is cloned into a vector,wherein the vector comprises at least one recognition site for arestriction endonuclease in proximity, for example, adjacent to wherethe nucleic acid sequence is cloned into, and wherein the recognitionsite produces a compatible end on cleavage.

In some aspects of the invention as disclosed herein, the use of anadapter or a linker can be used interchangeably, as will be understoodby the person of skill in the art.

As used herein, a “vector” is, for example, a plasmid, phage orphagemid, as will be understood by one of skill in the art. A vector asis understood by one of skill in the art to contain an origin ofreplication (“ori”) for DNA replication in a host organism (for example,E. coli). As used herein, “cloning” is the propagation of a nucleic acidsequence in a vector in a viable host cell, such as E. coli, as will beunderstood by one of skill in the art.

A variety of in vitro amplification methods are known in the art,including the polymerase chain reaction, “PCR”, and amplificationmethods that can be performed under isothermal conditions, collectivelyreferred to as “isothemal amplification”, which include, for example,rolling circle amplification (RCA), strand displacement amplification(SDA), multiple displacement amplification (MDA), and methods involvingthe use of a DNA dependent RNA polymerase (such as T7 RNA polymerase)and RNaseH. Compositions comprising paired tags and introduced nucleicacid sequences, such as linkers, adapters, or vectors can readily beamplified in vitro by using such methods. Furthermore, it is wellunderstood in the art that nucleic acid sequences may be amplified onsubstrates if one of the primers used in the amplification isimmobilized on the substrate.

In another embodiment of the invention, a method is provided forproducing a paired tag from a nucleic acid sequence, wherein the nucleicacid sequence comprises two restriction endonuclease recognition sitesspecific for a restriction endonuclease that cleaves the nucleic acidsequence distally to the restriction endonuclease recognition site, andat least two restriction endonuclease recognition sites specific for arare cutting restriction endonuclease. In one embodiment, endonucleaserecognition sites specific for a rare cutting restriction endonucleaseoccur minimally in a sequence (e.g. once, twice, etc.) are specificallyrecognized by a single rare (unique) cutting restriction endonuclease.In another embodiment, endonuclease recognition sites specific for arare cutting restriction endonuclease are specifically recognized bymultiple rare cutting restriction endonuclease. Thus, in one embodimentof the invention, a method is provided for producing a paired tag from anucleic acid sequence comprising cleaving the nucleic acid sequenceusing the restriction endonuclease that cleaves the nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a 5′ end tag and a 3′ end tag from the nucleic acidsequence. The 5′ end tag is joined with the 3′ end tag of the nucleicacid sequence to produce a paired tag from the nucleic acid sequence.The paired tag can be further cleaved with a rare cutting restrictionendonuclease, which produces a paired tag having compatible ends.

In an alternative embodiment, the present invention is drawn to a methodfor producing a paired tag from a nucleic acid sequence that comprisesat least one restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence distallyto the restriction endonuclease recognition site, and at least tworestriction endonuclease recognition sites specific for a rare cuttingrestriction endonuclease. The nucleic acid sequence is cleaved with therare cutting restriction endonuclease restriction endonuclease toproduce nucleic acid sequence fragments that have compatible ends andwhich nucleic acid sequence fragments comprise at least one restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves distally to the recognition site. The fragments areintramolecularly ligated to produce a circularized nucleic acidsequence. The circularized nucleic acid sequences are cleaved with therestriction endonuclease that cleaves the nucleic acid sequence distallyto the restriction endonuclease recognition site which results in theproduction of a paired tag comprising a 5′ end tag of the nucleic acidsequence and a 3′ end tag of the nucleic acid sequence.

A nucleic acid sequence that comprises two restriction endonucleaserecognition sites specific for a restriction endonuclease that cleavesthe nucleic acid sequence distally to the restriction endonucleaserecognition site, and/or at least one restriction endonucleaserecognition sites specific for a rare cutting restriction endonucleasecan be naturally-occurring, or prepared using techniques that arestandard in the art. Methods for introducing into the 5′ end and/or intothe 3′ end of a nucleic acid sequence fragment a restrictionendonuclease recognition site are well known in the art. For example, inone embodiment, a method for introducing into the 5′ end and/or into the3′ end of a nucleic acid sequence fragment a restriction endonucleaserecognition site comprises joining (e.g., ligating or annealing) to the5′ end and/or to the 3′ end a nucleic acid sequence that comprises therestriction endonuclease recognition site or, alternatively, forms therestriction endonuclease recognition site once joined to the 5′ endand/or to the 3′ end of the nucleic acid sequence fragment. In anotherembodiment, a method for introducing a restriction endonucleaserecognition site into the 5′ end and/or into the 3′ end of a nucleicacid sequence fragment comprises cloning the nucleic acid sequencefragment into a vector, wherein the 5′ end and/or 3′ end of the nucleicacid sequence fragment are cloned adjacent to one or more restrictionendonuclease recognition sites present in the vector. Alternatively, inanother embodiment, a method for introducing a restriction endonucleaserecognition site into the 5′ end and/or into the 3′ end of a nucleicacid sequence fragment comprises cloning the nucleic acid sequencefragment into a vector, wherein the 5′ end and/or 3′ end of the nucleicacid sequence fragment once cloned into the vector produces one or morerestriction endonuclease recognition sites at the 5′ end and/or 3′ endof the nucleic acid sequence fragment.

A nucleic acid sequence fragment can be prepared by a variety ofmethods. These methods are generally referred to herein as the“fragmenting” of a nucleic acid sequence. For example, fragmenting of anucleic acid sequence can be achieved by shearing (e.g. by mechanicalmeans such as nebulization, hydrodynamic shearing through a smallorifice, or sonication) the nucleic acid sequence or digesting thenucleic acid sequence with an enzyme, such as a restriction endonucleaseor a non-specific endonuclease. The nucleic acid sequence fragmentsobtained can be of any size (e.g., molecular weight, length, etc.). Inone embodiment, nucleic acid sequence fragments of a specific size(e.g., approximately greater than about 1 mb, about 200 kb, about 100kb, about 80 kb, about 40 kb, about 20 kb, about 10 kb, about 3 kb,about 1.5 kb, about 1 kb, about 500 bases, about 200 bases and rangesthereof) are isolated, for example, by gel electrophoresis purificationand extraction, by filtration methods, such as column filtration, or byother size fractionation methods that are standard in the art.

The production of a paired tag from a nucleic acid sequence has manyapplications. Provided in one embodiment of the invention is a methodfor characterizing a nucleic acid sequence. In a particular embodiment,characterizing a nucleic acid sequence comprises sequencing the pairedtags produced from the nucleic acid sequence. Sequencing methods arestandard in the art, and include, for example, traditional sequencingusing the Maxam and Gilbert technique or the Sanger method, or byhybridization to an array or microarray of known oligonucleotides on,for example, a chip. Alternative approaches include sequencing bysynthesis methods in which primer-template complexes are immobilized,for example, to a substrate such as a polymer, a magnetic bead, or asolid surface, and are extended using a DNA polymerase or DNA ligase inthe presence of labeled substrates such that the addition products canbe characterized to determine the DNA sequence.

In one embodiment, the nucleic acid sequence to be characterized is agenome. A genome is the genomic DNA of a cell or organism. In oneembodiment, the genome is of a prokaryote, eukaryote, plant, virus,fungus, or an isolated cell thereof. In another embodiment, the genomeis a known (previously characterized or sequenced) genome. In a furtherembodiment, the genome is an unknown (not previously characterized orsequenced) genome. In one embodiment, characterizing a genome compriseskaryotyping the genome. Karyotyping is the analysis of the genome of acell or organism. In another embodiment, characterizing the genomecomprises polymorphism discovery or genotyping to identify differencesbetween two or more nucleic acid sequences derived from differentsources.

In one embodiment of the invention, a method for characterizing anucleic acid sequence is provided which comprises fragmenting a nucleicacid sequence to produce a plurality of nucleic acid sequence fragmentshaving a 5′ end and a 3′ end. A restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site and a restriction endonuclease recognitionsite specific for a rare cutting restriction endonuclease are introducedinto the 5′ end and into the 3′ end (either upstream or downstream asappropriate) of each nucleic acid sequence fragment to produce modifiednucleic acid sequence fragments. The modified nucleic acid sequencefragments are cleaved with the rare cutting restriction endonucleasespecific for the previously introduced rare cutting restrictionendonuclease recognition site, which produces a plurality of nucleicacid sequence fragments having compatible ends. The fragments areintramolecularly ligated to produce a plurality of circularized nucleicacid sequences comprising the two restriction endonuclease recognitionsites specific for restriction endonucleases that cleave the nucleicacid fragment distally to the restriction endonuclease recognitionsites. The circularized nucleic acid sequences are cleaved at therestriction endonuclease recognition sites with the restrictionendonucleases specific for the restriction endonuclease recognitionsites to produce a plurality of paired tags comprising a 5′ end tag anda 3′ end tag of the nucleic acid fragment. These the paired tags arecharacterized, which thus characterizes the nucleic acid sequence ofinterest.

In an alternative embodiment of the invention, a method forcharacterizing a nucleic acid sequence comprises, fragmenting a nucleicacid sequence to produce a plurality of nucleic acid sequence fragmentshaving a 5′ end and a 3′ end. A restriction endonuclease recognitionsite specific for a restriction endonuclease that cleaves the nucleicacid fragment distally to the restriction endonuclease recognition siteis introduced into the 5′ end and into the 3′ end of each nucleic acidsequence fragment, thus producing a plurality of modified nucleic acidsequence fragments. The modified nucleic acid sequence fragments are,for example, cloned into a vector. The cloned nucleic acid sequencefragments are cleaved at the restriction endonuclease recognition sitesat the 5′ end and the 3′ end of the cloned nucleic acid sequencefragments using the restriction endonuclease that is specific for therestriction endonuclease recognition sites, which produces a 5′ end tagand a 3′ end tag of each cloned nucleic acid sequence fragment. The 5′end tag and a 3′ end tag of each cloned nucleic acid sequence fragmentare joined to produce a plurality of paired tags which can becharacterized, thereby permitting the characterizing of the nucleic acidsequence.

In another embodiment of the invention, a method for characterizing anucleic acid sequence comprises, fragmenting a nucleic acid sequence toproduce a plurality of nucleic acid sequence fragments having a 5′ endand a 3′ end. A restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid fragment distallyto the restriction endonuclease recognition site is introduced into the5′ end and into the 3′ end of each nucleic acid sequence fragment, thusproducing a plurality of modified nucleic acid sequence fragments. Themodified nucleic acid sequence fragments are intramolecularly ligated toproduce circularized modified nucleic acid sequence fragments.Intramolecular ligation can be achieved, for example, by emulsionligation. The circularized modified nucleic acid sequence fragments arecleaved at the restriction endonuclease recognition sites introduced atthe 5′ end and the 3′ end of the modified nucleic acid sequencefragments using the restriction endonuclease specific for therestriction endonuclease recognition sites, which produces a 5′ end tagand a 3′ end tag of each modified nucleic acid sequence fragment. The 5′end tag and a 3′ end tag of each nucleic acid sequence fragment arejoined (i.e., concatemerized) to produce a plurality of paired tags(i.e., a concatemer) which can be characterized, thereby permitting thecharacterizing of the nucleic acid sequence.

In a further embodiment of the invention, a method for characterizing anucleic acid sequence comprises, fragmenting a nucleic acid sequence toproduce a plurality of nucleic acid sequence fragments having a 5′ endand a 3′ end. Each nucleic acid sequence fragment is cloned to introduceinto the 5′ end and into the 3′ end of each cloned nucleic acid sequencefragment, a restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site. The clonedfragments are cleaved at the restriction endonuclease recognition sitesat the 5′ end and the 3′ end of each cloned nucleic acid sequencefragment using the restriction endonuclease that is specific for therestriction endonuclease recognition sites, thereby producing a 5′ endtag and a 3′ end tag of the cloned nucleic acid fragments. The 5′ endtag and the 3′ end tag of each cloned nucleic acid are joined to producea plurality of paired tags. These paired tags can now be characterized,thereby characterizing the nucleic acid sequence.

In another embodiment of the invention, a method for characterizing anucleic acid sequence comprises fragmenting a nucleic acid sequence toproduce a plurality of nucleic acid sequence fragments having a 5′ endand a 3′ end. One or more linkers and/or adapters are joined to theends, and an intramolecular ligation step is performed to produce aplurality of circularized nucleic acid sequences, wherein an interveninglinker is introduced between the 5′end and the 3′end a nucleic acidsequence fragment. The circularized molecules are fragmented by randomshearing or by other means and an adapter is joining to the ends of thefragments to produce a plurality of linear nucleic acid moleculeswherein an adapter is introduced at each end. The resulting nucleic acidmolecules containing the 5′ and 3′ends of a nucleic acid sequencefragment (paired tag) are amplified by PCR using a universal primercomplementary to the adapter sequences. The paired tags are thencharacterized, thereby characterizing the nucleic acid sequence.

In an alternative embodiment of the invention a method forcharacterizing a nucleic acid sequence comprises fragmenting a nucleicacid sequence to produce a plurality of nucleic acid sequence fragmentshaving a 5′ end and a 3′ end. One or more linkers and/or adapters arejoined to the ends, and an intramolecular ligation is performed toproduce a plurality of circularized nucleic acid sequences, wherein anintervening first linker is introduced between the 5′end and the 3′end anucleic acid sequence fragment. The circularized molecules arefragmented by random shearing or by other means, and adapters are joinedto the ends of the fragments. A second intramolecular ligation isperformed to produce a plurality of circularized nucleic acid sequences,wherein an intervening second linker is introduced between the ends ofthe fragments, wherein the second linker comprises two priming sites.The molecules containing the 5′ and 3′ends of a nucleic acid sequencefragment (the paired tag) are amplified by PCR using two differentprimers that are complementary to the priming sites in the secondlinker. The paired tags are then characterized, thereby characterizingthe nucleic acid sequence.

In another embodiment of the invention a method for characterizing anucleic acid sequence comprises fragmenting a nucleic acid sequence toproduce a plurality of nucleic acid sequence fragments having a 5′ endand a 3′ end. One or more linkers and/or adapters are joined to theends, and an intramolecular ligation is performed to produce a pluralityof circularized nucleic acid sequences, wherein an intervening firstlinker is introduced between the 5′end and the 3′end a nucleic acidsequence fragment. The circularized molecules are fragmented by randomshearing or by other means, and adapters are joined to the ends of thefragments. A second intramolecular ligation is performed to produce aplurality of circularized nucleic acid sequences, wherein an interveningsecond linker is introduced between the ends of the fragments, whereinthe second linker comprises two priming sites separated by arare-cutting restriction endonuclease cleavage site. The moleculescontaining the 5′ and 3′ends of a nucleic acid sequence fragment (thepaired tag) are cleaved using a rare-cutting restriction endonucleasethat recognizes the cleavage site in the linker. Linearization of thecircular DNA molecules is not required, but improves the efficiency ofPCR amplification in the next step. The resulting linear molecules areamplified by PCR using two different primers that are complementary tothe priming sites in the second linker. The paired tags are thencharacterized, thereby characterizing the nucleic acid sequence.

In an alternate embodiment of the invention a method for characterizinga nucleic acid sequence comprises fragmenting a nucleic acid sequence toproduce a plurality of nucleic acid sequence fragments having a 5′ endand a 3′ end. One or more linkers and/or adapters are joined to theends, and an intramolecular ligation is performed to produce a pluralityof circularized nucleic acid sequences, wherein an intervening firstlinker containing a sequence or chemical moiety that enables affinitycapture is introduced between the Send and the 3′end a nucleic acidsequence fragment. The circularized molecules are fragmented by randomshearing or by other means, and adapters are joined to the ends of thefragments. The molecules containing the 5′ and 3′ends of a nucleic acidsequence fragment are purified by affinity capture using a reagentspecific for the first linker. A second intramolecular ligation is thenperformed to produce a plurality of circularized nucleic acid sequences,wherein an intervening second linker is introduced between the ends ofthe fragments, wherein the second linker comprises two priming sites.The molecules containing the 5′ and 3′ends of a nucleic acid sequencefragment (the paired tag) are amplified by PCR using two differentprimers that are complementary to the priming sites in the secondlinker. The paired tags are then characterized, thereby characterizingthe nucleic acid sequence.

A second purification step, for example, by affinity capture using areagent specific for a sequence in the first linker, may be added priorto PCR amplification. Alternatively, the first purification step couldbe omitted and a single purification step could be performed prior toPCR amplification.

In another embodiment of the invention a method for characterizing anucleic acid sequence comprises fragmenting a nucleic acid sequence toproduce a plurality of nucleic acid sequence fragments having a 5′ endand a 3′ end. One or more linkers and/or adapters are joined to theends, and an intramolecular ligation is performed to produce a pluralityof circularized nucleic acid sequences, wherein an intervening firstlinker containing a sequence or chemical moiety that enables affinitycapture is introduced between the 5′end and the 3′end a nucleic acidsequence fragment. The circularized molecules are fragmented by randomshearing or by other means, and adapters are joined to the ends of thefragments. The molecules containing the 5′ and 3′ends of a nucleic acidsequence fragment are purified by affinity capture using a reagentspecific for the first linker. A second intramolecular ligation is thenperformed to produce a plurality of circularized nucleic acid sequences,wherein an intervening second linker is introduced between the ends ofthe fragments, wherein the second linker comprises two priming sitesseparated by a rare-cutting restriction endonuclease cleavage site. Themolecules containing the 5′ and 3′ends of a nucleic acid sequencefragment (the paired tag) are cleaved using a rare-cutting restrictionendonuclease that recognizes the cleavage site in the linker.Linearization of the circular DNA molecules is not required, butimproves the efficiency of PCR amplification in the next step. Theresulting linear molecules are amplified by PCR using two differentprimers that are complementary to the priming sites in the secondlinker. The paired tags are then characterized, thereby characterizingthe nucleic acid sequence. When two intramolecular ligation steps areperformed, both the 5′end and the 3′end of a nucleic acid sequencefragment paired tag can be sequenced from the same DNA strand by usingseparate primers that are complementary to the sequences in the firstand second linkers. The use of two distinct PCR primers enablesamplification on a substrate (e.g., on the surface of a chip or amagnetic bead) wherein only one of the two primers is attached to thesubstrate, which results in all of the molecules being amplified in aunique orientation with respect to the substrate.

In a further embodiment of the invention, a method is provided foridentifying nucleic acid sequences that encode at least two interactingproteins. Typically, this method comprises combining (1) a first vectorthat comprises a nucleic acid sequence that encodes a first protein thatinteracts with a second protein and a first restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site and (2) a second vector that comprises anucleic acid sequence that encodes the second protein and a secondrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site. Typically, thiscombination of vectors is maintained under conditions in which the firstprotein and the second protein are expressed and interact. Onceinteracting first and second interacting proteins are identified, thefirst and second vectors encoding same are selected for identification.Identification of interacting proteins use methods that are standard inthe art (e.g., 2 or 3 hybrid systems such as yeast, bacteria andmammalian). The vectors encoding the two interacting proteins are joinedto form a contiguous nucleic acid sequence which comprises the nucleicacid sequence that encodes the first protein, the first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, the nucleic acid sequencethat encodes the second protein, and the second restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site. This contiguous nucleic acid sequence iscleaved at the first and second restriction endonuclease recognitionsites with restriction endonucleases that cleave the contiguous nucleicacid sequence distally to the restriction endonuclease recognition sitesto produce a 5′ end tag and a 3′ end tag of the contiguous nucleic acidsequence. The 5′ end tag is joined to the 3′ end tag to produce a pairedtag which can be sequenced, thereby identifying the nucleic acidsequences that encode the at least two interacting proteins. In oneembodiment, the paired tag produced from one combination of vectors thatencode at least two interacting proteins can be joined with one or morepaired tags produced from other combinations of vectors that encode atleast two interacting proteins, to produce a concatemer that can besequenced. Sequencing of such concatemers provides for high throughputanalyses and increased efficiency.

In another embodiment of the invention, a method for identifying nucleicacid sequences that encode at least two interacting proteins isprovided. This method provides combining a first vector which cancomprise (1) a nucleic acid sequence that encodes a first protein thatinteracts with a second protein and (2) a first restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site and a second vector which can comprise (1)a nucleic acid sequence that encodes the second protein, and (2) asecond restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site, whichproduces a combination. The combination is maintained under conditionsthe first protein and the second protein are expressed and interact. Thefirst vector and second vector are joined to form a contiguous nucleicacid sequence that comprises (i) the nucleic acid sequence that encodesa first protein that interacts with a second protein, (ii) the firstrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, (iii) the nucleic acidsequence that encodes the second protein, and (iv) the secondrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site. The contiguous nucleicacid sequence is sequenced, thereby identifying nucleic acid sequencesthat encode at least two interacting proteins.

In an alternative embodiment of the invention, a method for identifyingnucleic acid sequences that encode at least two interacting proteins isprovided. The method combines a first vector which can comprise (1) anucleic acid sequence that encodes a first protein that interacts with asecond protein, and (2) a first restriction endonuclease recognitionsite specific for a restriction endonuclease that cleaves the nucleicacid sequence fragment distally to the restriction endonucleaserecognition site and a second vector which can comprise (1) a nucleicacid sequence that encodes the second protein and (2) a secondrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, which produces acombination. The combination is maintained under conditions in which thefirst protein and the second protein are expressed and interact. Thefirst vector is joined with the second vector, thereby forming acontiguous nucleic acid sequence that comprises (i) the nucleic acidsequence that encodes a first protein that interacts with a secondprotein, (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, (iii) the nucleic acid sequence that encodes the second proteinand (iv) the second restriction endonuclease recognition site specificfor a restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site. Thefirst restriction endonuclease recognition site and the secondrestriction endonuclease recognition site in the contiguous nucleic acidsequence are cleaved with restriction endonucleases that cleave thecontiguous nucleic acid sequence distally to the restrictionendonuclease recognition sites, thereby producing a paired tagcomprising a 5′ end tag and a 3′ end tag of the contiguous nucleic acidsequence. The paired tag is sequenced, thereby identifying nucleic acidsequences that encode at least two interacting proteins.

In a further embodiment of the invention, a method is provided foridentifying a plurality of nucleic acid sequences that encode at leasttwo interacting proteins. In a particular embodiment, the methodprovides for screening multiple nucleic acids, such as, for example, alibrary of nucleic acids, as will be appreciated by one of skill in theart. The method comprises combining a plurality of first vectors eachcan comprise (1) a nucleic acid sequence that encodes a first proteinthat interact with a second protein and (2) a first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site and a plurality of secondvectors each comprising (1) a nucleic acid sequence that encodes thesecond protein and (2) a second restriction endonuclease recognitionsite specific for a restriction endonuclease that cleaves the nucleicacid sequence fragment distally to the restriction endonucleaserecognition site, thereby producing a combination comprising a pluralityof first vectors and a plurality of second vectors. The combination ismaintained under conditions in which the plurality of first vectorsencoding a first protein and the plurality of second vectors encoding asecond protein are expressed and the first protein and second proteininteract. The first vectors are joined with the second vectors, whereinthe first vectors and second vectors encode interacting proteins,thereby forming a plurality of contiguous nucleic acid sequences. Theplurality of contiguous nucleic acid sequences each comprise (i) thenucleic acid sequence that encodes a first protein that interacts with asecond protein, (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, (iii) the nucleic acid sequence that encodes the second proteinand (iv) the second restriction endonuclease recognition site specificfor a restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site. Ineach contiguous nucleic acid sequence, the first restrictionendonuclease recognition site and the second restriction endonucleaserecognition site are cleaved with the restriction endonucleases thatcleave the contiguous nucleic acid sequence distally to the restrictionendonuclease recognition sites, thereby producing a plurality of pairedtags comprising a 5′ end tag and a 3′ end tag of the contiguous nucleicacid sequence. The paired tags are joined and sequenced, therebyidentifying a plurality of nucleic acid sequences that encode at leasttwo interacting proteins.

Also provided in the invention is a method for identifying nucleic acidsequences that encode at least two interacting proteins comprisingcombining a first vector which can comprise (1) a nucleic acid sequencethat encodes a first protein that interacts with a second protein and(2) a first restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site and (3) asecond restriction endonuclease recognition site, which in oneembodiment, can be adjacent to the first restriction endonucleaserecognition site and a second vector which can comprise (1) a nucleicacid sequence that encodes the second protein (2) a third restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and (3) a fourth restrictionendonuclease recognition site, which in one embodiment, can be adjacentto the third restriction endonuclease recognition site, therebyproducing a combination. The combination is maintained under conditionsin which the first protein and the second protein are expressed andinteract. The first vector is joined with the second vector, therebyforming a contiguous nucleic acid sequence that comprises (i) thenucleic acid sequence that encodes a first protein that interacts with asecond protein, (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, (iii) the second restriction endonuclease recognition site, (iv)the nucleic acid sequence that encodes the second protein, (v) the thirdrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site, and (vi) the fourthrestriction endonuclease recognition site. The second restrictionendonuclease recognition site and the fourth restriction endonucleaserecognition site in the contiguous nucleic acid sequence are cleavedwith restriction endonucleases to produce compatible ends in thecontiguous nucleic acid sequence. The nucleic acid sequence ismaintained under conditions in which the compatible ends in thecontiguous nucleic acid sequence intramolecularly ligate, therebyproducing a circularized nucleic acid sequence. The circularized nucleicacid sequence is sequenced, thereby identifying nucleic acid sequencesthat encode at least two interacting proteins.

In a further embodiment of the invention, a method for identifyingnucleic acid sequences that encode at least two interacting proteins isprovided. The method comprises combining a first vector which cancomprise (1) a nucleic acid sequence that encodes a first protein thatinteracts with a second protein, (2) a first restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site; and (3) a second restriction endonucleaserecognition site, which in one embodiment, can be adjacent to the firstrestriction endonuclease recognition site and a second vector which cancomprise (1) a nucleic acid sequence that encodes the second protein (2)a third restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site and (3) afourth restriction endonuclease recognition site, which in oneembodiment, can be adjacent to the third restriction endonucleaserecognition site, thereby producing a combination. The combination ismaintained under conditions in which the first protein and the secondprotein are expressed and interact. The first vector is joined with thesecond vector, thereby forming a contiguous nucleic acid sequence thatcomprises (i) the nucleic acid sequence that encodes a first proteinthat interacts with a second protein, (ii) the first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, (iii) the second restrictionendonuclease recognition site, (iv) the nucleic acid sequence thatencodes the second protein, (v) the third restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site and (vi) a fourth restriction endonucleaserecognition site. The second restriction endonuclease recognition siteand the fourth restriction endonuclease recognition site in thecontiguous nucleic acid sequence are cleaved with restrictionendonucleases, thereby producing compatible ends in the contiguousnucleic acid sequence. The contiguous nucleic acid sequence ismaintained under conditions in which the compatible ends in thecontiguous nucleic acid sequence intramolecularly ligate, therebyproducing a circularized nucleic acid sequence. The first restrictionendonuclease recognition site and the third restriction endonucleaserecognition site in the circularized nucleic acid sequence are cleavedwith restriction endonucleases that cleave the circularized nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a paired tag comprising a 5′ end tag and a 3′ end tagof the circularized nucleic acid sequence. The paired tag is sequenced,thereby identifying nucleic acid sequences that encode at least twointeracting proteins.

Further provided in the invention is a method for identifying aplurality of nucleic acid sequences that encode at least two interactingproteins. The method comprises combining a plurality of first vectorseach can comprise (1) a nucleic acid sequence that encodes a firstprotein that interacts with a second protein, (2) a first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site, and (3) a second restrictionendonuclease recognition site, which in one embodiment, can be adjacentto the first restriction endonuclease recognition site and a pluralityof second vector each comprising (1) a nucleic acid sequence thatencodes the second protein, (2) a third restriction endonucleaserecognition site specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site and (3) a fourth restriction endonucleaserecognition site, which in one embodiment, can be adjacent to the thirdrestriction endonuclease recognition site, thereby producing acombination comprising a plurality of first vectors and a plurality ofsecond vector. The combination is maintained under conditions in whichthe plurality of first vectors encoding a first protein and theplurality of second vectors encoding a second protein are expressed andthe first protein and second protein interact. The first vectors arejoined the second vectors, wherein the first vectors and second vectorsencode interacting proteins, thereby forming a plurality of contiguousnucleic acid sequences that each can comprise (i) the nucleic acidsequence that encodes a first protein that interacts with a secondprotein, (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, (iii) the second restriction endonuclease recognition site, whichin one embodiment, can be adjacent to the first restriction endonucleaserecognition site, (iv) the nucleic acid sequence that encodes the secondprotein, (v) the third restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite, and (vi) the fourth restriction endonuclease recognition site,which in one embodiment, can be adjacent to the third restrictionendonuclease recognition site. The second restriction endonucleaserecognition site and the fourth restriction endonuclease recognitionsite in the contiguous nucleic acid sequence are cleaved withrestriction endonucleases that produce compatible ends. The contiguousnucleic acid sequence with compatible ends is maintained underconditions in which the compatible ends intramolecularly ligate, therebyproducing a circularized nucleic acid sequence that encodes a sequencefrom the first protein and a sequence from the second protein thatinteract with each other. The first restriction endonuclease recognitionsite and the third restriction endonuclease recognition site in eachcircularized nucleic acid sequence is cleaved with restrictionendonucleases that cleave each contiguous nucleic acid sequence distallyto the restriction endonuclease recognition sites, thereby producing aplurality of paired tags comprising a 5′ end tag and a 3′ end tag of thecircularized nucleic acid sequence. The paired tags are joined andsequenced, thereby identifying a plurality of nucleic acid sequencesthat encode at least two interacting proteins.

In one embodiment of the invention, joining is a site-specificintermolecular recombination. In another embodiment, joining is asite-specific intermolecular recombination at mutant site specificrecombinase recognition sites, wherein recombination produces recombinedsites having a decreased ability to subsequently recombine. In a furtherembodiment of the invention, the joining is site-specific intermolecularrecombination between a lox71 site and a lox66 site. In a still furtherembodiment, cleaving the second restriction endonuclease recognitionsite and cleaving the fourth restriction endonuclease recognition sitein the contiguous nucleic acid sequence releases a fragment containing arecombined site-specific recombinase recognition site between thenucleic acid sequence that encodes a sequence from the first protein anda sequence from the second protein that interact with each other.

EXAMPLE 1 Whole Genome Assembly

The whole genome shotgun sequencing, assembly and finishing paradigm isgenerally the strategy of choice for microbial and fungal genomesequencing. Contrary to the expectations of some, recent advances in thedevelopment and application of whole genome assembly (WGA) software,such as Arachne, the Celera Assembler, Phusion, or Jazz, have alsodemonstrated that it is straightforward to produce a high qualityassembly of plant and mammalian genomes using such tools (Mural, Adamset al. 2002; Jaffe, Butler et al. 2003). The cost-advantages andsimplicity of the whole genome approach relative to a BAC based orhybrid sequencing strategy argue strongly for its continued developmentand application in future sequencing projects. One problem with the BACbased approaches is the high cost and operational burden associated withthe production of 15,000-25,000 individual BAC subclone libraries, the15-20% waste associated with re-sequencing the vector as well as theunavoidable E. coli contamination, the need to deal with transposon andbacteriophage insertions, and the 20-50% waste in redundant sequencingof BAC overlaps. Although these costs can be reduced by sequencing theBACs at low coverage (using a hybrid BAC/WGS strategy, for example) orby using a pooling strategy, they cannot be eliminated. The need togenerate a physical map by using restriction digest fingerprinting or bycomplex pooling and sequence based mapping strategies adds additionalcost and operational overhead.

For genomic sequencing and assembly, the preferred library that isconstructed has a narrow fragment size distribution (Jaffe et al.).Using restriction enzyme digestion can lead to a reduced representationlibrary because of the difficulty in size selection of arestriction-digested genome (Altshuler et al.). For a particular sizerange of genomic fragments to be achieved, restriction enzymerecognition sites are necessary to be spaced appropriately in order toachieve the desired results. In contrast, physical shearing permits thewhole genome to be fragmented into a particular size range regardless ofwhere restriction enzyme recognition sites are found in the genome.Additionally, using in vivo library construction requires the library tobe cloned into vectors and transformed into the preferred host E. coli.This results in a cloning bias which typically under-represents AT-richregions of the genome (Mead et al.). In a preferred method, theproduction of a genomic library would not be dependent on the use ofvectors and E. coli, thereby minimizing cloning biases. For example,performing emulsion ligations in combination with Emulsion PCR avoidsthe necessity of E. coli and permits DNA amplification on a solidsupport for future sequencing.

A critical question regarding the WGS approach is whether it is possibleto generate enough long range scaffolding information to avoidmisassemblies of genomic regions involving complex repeats, significantlevels of allelic polymorphism, or recent segmental duplications. Oneaim is to provide a reliable sequence-derived genome map that cansupport the accurate selection of clones to finish any desired region ofthe genome. As pointed out by Jaffe et al., (supra), the C57BL6/J mousegenome has certain characteristics that may have expedited the wholegenome assembly process. These include the inbred status and theapparently low number of recent segmental duplications compared to thehuman genome. In addition, a significant number of large insert readswere generated (about 4-fold clone coverage from 10 kb inserts, 9-foldfrom 40 kb inserts, and 14 fold from 200 kb inserts), although this wasa strategic decision that could be applied to any genome. As statedabove, the recent improvements in the ability to produce paired endsequences (paired tags) from large insert clones make it possible tosignificantly increase the number of such sequences compared to thatused in the mouse project. A more detailed discussion of issues relatingto segmental duplications and sequence polymorphism is presented below.

Clearly, independent mapping data (genetic or RH markers, or BAC overlapdata, for example) is helpful for placing supercontigs in relation toeach other, especially where BAC end data are missing or ambiguous.However, it is possible to generate such information by other means (seebelow), or to collect the necessary data to disambiguate such regionsthrough targeted post-assembly mapping efforts (for example, usingsequence data from unmapped supercontigs to identify overlapping clonesdirectly or to augment other existing mapping resources). The methodprovided herein increases the number of Fosmid ends and other long rangelinks such that they occur at a spacing of at least one every 500 bp inthe assembly, more than four times the density used in the mouseproject, and four times the number required to achieve statisticalclosure of supercontigs.

Mathematical modeling studies (Ru-Fang Yeh, 1999) indicate that genomeclosure, as expressed in terms of supercontig length, can besignificantly accelerated by using a high level of clone coverage and abroad range of insert sizes in large whole genome shotgun projects. Thisis illustrated in FIG. 1 (computed from the Yeh model), in which thesigmoidal curves indicate the theoretical length of supercontigs thatwould be produced using our proposed mix of insert sizes (green curve)versus a single insert size (blue curve), for a non-repetitive 3 Gbgenome and a 100% paired end rate.

Supercontig closure can be significantly accelerated by using high clonecoverage with a mix of insert sizes.

As shown in FIG. 1, there is a significant increase in the expectedcontig length (from ˜98 kb to ˜567 kb) and decrease in contig number(from ˜30,000 to ˜5,300) as the sequence coverage goes up from about 7to about 9 fold coverage (approximately equivalent to an increase inPhred Q20 coverage from about 6 to about 8 fold).

Experiments can determine the effect of insert size and modification ofdistance to improve the assembly. By focusing on accurate sizing oflibraries from which reads are derived, the assembly based on morecareful sizing of inserts is refined. For the special case ofcomparative sequencing applications within a species it is possible todefine the distance constraints very precisely based on comparison ofthe paired end data to a reference sequence. All WGS reads can bepre-processed this way and entered into the assembly program.

Given the high level of shotgun coverage and the large amount of longrange linking information that is obtained, genomic assemblies aregenerated with an average contig length of approximately 125 kb, andwith supercontigs spanning a large proportion of the euchromaticchromosome arms. Gap in the large insert scaffold can be bridged throughthe generation and mapping of paired end GST sequences. Thus, completionof the project having very few clone gaps remaining will be achieved.

Segmental Duplications

FIG. 2 graphs the information on the numbers of segmental duplicationsidentified in the rat genome by Evan Eichler and colleagues versus the %identity of the cognate pairs (referred to here as duplicons). Thenumber of duplications in the rat genome is similar to that in the humangenome, about 3.7% vs about 4%, respectively. It is clear from the graphthat there is a trend towards stronger similarity as the size of theduplicated region goes up. This phenomenon has been describedpreviously, and presumably reflects degradation of segmentalduplications over evolutionary timescales. Notably, more than 99.9% ofthe duplications are less than 70 kb in size, and these are generallyless than 98% identical.

For duplications up to 70 kb in size, the large number of Fosmidsequence links generated in this assembly method (occurring every 500 bpor so; less than the average read length), will allow the Arachnesoftware to connect nearly all of the sequence reads falling within theduplicated region to the unique sequences flanking it on either side(the Fosmid links to either side will still meet at the center). This,in turn, will allow clear segregation of the four chromosomal haplotypeswithin each pair of duplicons, considering especially the high expectedaccuracy of the component sequences (˜4 fold Q20 coverage).

Larger duplications that collapsed in the assembly can be detected asextended regions with high coverage (˜16×Q20), and are readilydeconvoluted using the Fosmid and BAC-end information to link out to theunique sequences on each side. To correctly segregate and precisely mapthe two nearly identical sequences for a particular duplication ofspecial interest, the representative BACs from each duplicon can be usedto generate finished sequences.

Polymorphism

Sequences with polymorphism rates that fall significantly below themismatch threshold settings of the assembly software (as implied above;typically about 1% mismatch for bases of Phred 20 quality and about 0.2%mismatch for bases of Phred 30 quality) will be well tolerated andcorrectly assembled by the software, in most cases. In the resultingassembly, these regions will be characterized by high-qualitydiscrepancies in contigs where the assembly is otherwise stronglysupported by mate pair information, allowing SNPs to be detected andcharacterized.

In the case of Anopheles, the Celera assembler was tuned to accept ahigher mismatch frequency than usual to allow most regions with ahigh-density of SNPs to be assembled correctly (Holt, Subramanian et al.2002). However, some regions remained where both haplotypes wereassembled into separate contigs in the same supercontig causing “pseudotandem duplication”, or where one haplotype was left out of thesupercontig as an entirely separate element (see FIG. 3). Anunderstanding of the origin of these effects and their consequences interms of mate pair conflicts between the associated contigs, however,allows detection and correction of such sequences. For example, a contigthat represents a correctly assembled region with low heterozygositywould have mate pair bridges to two separate contigs representing thetwo different haplotypes of an adjoining region with highheterozygosity. These mate pair conflicts will force the assembler toeither shift one of the polymorphic contigs out of position or toexclude it from the supercontig. Algorithmic improvements can be made tothe assembly software to deal with such situations automatically. Otherproblems due to genomic inversions, or large palindromic sequences, canbe detected by a different pattern of characteristic mate pairconflicts.

Regular assemblies of the reads will help monitor the quality oflibraries on an ongoing basis. Assemblies using Arachne 2.0.1 can bemonitored for number and N50 length of contigs, number and N50 length ofsupercontigs, average fold coverage, for the occurrence of contigs withlocal coverage in a sliding window that deviates significantly from theexpected levels, and for mate pair conflicts as described above. Ifthere are previously sequenced clones from the genome, comparisons tothese regions can be conducted using Arachne to evaluate the assemblyquality. Arachne's output assists in detecting deviations of observedK-mer frequencies versus expected, for example, which can be monitored.

New Sequenced Based Mapping Tools

It will be useful to develop sequence-based mapping tools that cancompliment the WGS and BAC end sequencing data without addingsignificant incremental cost or operational overhead.

A high density of BAC- and Fosmid-end sequence pairs can obviate theneed for independent mapping data in most regions of the genome byproviding a highly redundant network of long-range clone links. However,it is possible that certain regions that are incompatible with thesecloning systems would not be represented. Wherever such sequences occurin the genome, a persistent break in the large insert scaffold will beencountered. A linking strategy to jump over such sequences, such asthat applied by Celera to produce “virtual 50 kb clones” (Venter, Adamset al. 2001) can be used to overcome these instances. However, byreplacing the standard restriction based jumping library strategy with anovel long SAGE-like approach (Velculescu, Zhang et al. 1995), largenumbers of long range links (from about 20 to about 100 kb) can becreated using short sequence tags (from about 20 to about 25 bases) withapproximately 20 times the efficiency of standard paired end sequencing.By using such a strategy, a genomic tag spacing of 500 bp can begenerated with only about 300,000 sequencing reads. Unlike BAC- orFosmid-end sequencing, the tags can be cloned in high copy numbervectors that are compatible with our current high copy prepping methods.In addition, short genomic sequence stretches, punctuated by linkersequences, may allow efficient generation of tag pairs for AT-richsequences that are often difficult to clone in large insert E. colibased vector systems. Thus, the method provides long range linkinginformation where it is otherwise very difficult to generate.

This method efficiently produces paired tag pairs from randomly shearedor restriction digested fragment ends with any desired length up toabout 100 kb, ensuring that only contiguous paired end tags aregenerated (see, for example, FIG. 4). This method is also referred toherein as Paired Genomic Sequence Tagging, or Paired GST. Paired GSTlibraries are distinctly different from conventional Digital karyotyping(“DK”) libraries in that the paired tags are generated from the ends ofindividual genomic fragments.

In one method, several different restriction enzymes with hexanucleotiderecogition sites that generate 4 base overhangs are used (for example,to avoid sequence bias) to partially digest the target DNA, creating acollection of fragments averaging 40 kb in size. The genomic fragmentsare treated with a single-strand specific endo- or exonuclease to removethe single stranded overhangs, destroying the restriction sites andleaving one base of the original hexanucleotide recognition site at eachend of the fragments. This method generates sequence tags ofapproximately 25 base if a MmeI site is juxtaposed to the ends of thefragments because the reach of MmeI is 20 bases and 5 bases can beinferred from the destroyed restriction sites. The use of restrictionenzymes can be avoided (e.g., the starting DNA can be fragmented byshearing) at the cost of 5 bases in the tag length. The method utilizesin vitro paired tag generation via intramolecular ligation in dilutesolution and does not necessarily require any passage of large fragmentsthrough E. coli, thereby avoiding any cloning bias. The resulting tagpairs will bridge any persistent gaps in the high coverage plasmid andFosmid/BAC clone scaffold.

Although tags of about 25 bases will generally be unique in a 3 Gbgenome (frequency of 1 in 10¹⁵), tags with one or both ends falling in arepeated sequence may not be used to reliably force a join between twocontigs or supercontigs. However, a genomic spacing of approximately 50kb between tag pair elements (insert length) and an average spacing ofapproximately 500 bases between tags in the genome would result in anaverage of approximately 50 redundant links across any given point inthe genome. Even if half of these tag pairs must be excluded forassembly purposes due to repeats, the remaining linking informationacross any given point would equate to approximately 1,250 bases ofunique sequence information (approximately 25 paired tags ofapproximately 50 bases each), and would be mutually confirming,resulting in an astronomically small probability of joining error. Tagpairs with only one repeated end can be used later to confirm joins thatwere made during assembly using the unique information.

EXAMPLE 2 Paired Genome Sequence Tag Method

Typically, a collection of genomic DNA fragments is produced byfragmentation using one or more restriction endonucleases, or byshearing, with subsequent repair of the ends to produce blunt-endedfragments. Fragments of a specific size range are purified by gelelectrophoresis, followed by extraction from a gel slice byelectroelution, extraction with chaotropic salts and glass beads, orenzymatic dissolution of the gel followed by phenol extraction andethanol precipitation. The fragments are ligated to an adaptercontaining a type IIs restriction enzyme site juxtaposed to a blunt endand the resulting circularized products are subsequently digested withthe enzyme to create short tags specific to the ends of the DNAfragment. These tags, which remain connected to each other through theprocess via the adapter are ligated to form concatemers of paired tags.The concatemers are sequenced and the paired tags extracted from thesequence. The paired information can be used to improve shotgun genomeassemblies or detect regions of a genome that have beenrearranged/translocated, amplified and/or deleted.

In one method, adapters containing a TypeIIs site followed by arare-cutting restriction site are ligated on to the DNA in a manner thatbrings the TypeIIs site immediately next to the end of the prepared DNA.The adapters are created in such a way as to stop long concatemers ofadapters from forming during the ligation process. Excess unligatedlinkers are removed using gel purification, solid phase reversibleimmobilization (SPRI), filtration, or selective precipitation. Theadapted DNA is digested with the rare-cutting restriction enzymegenerating compatible sites at the end of each adapted DNA strand. TheDNA is ligated at a molarity encouraging high intramolecular ligationrather than intermolecular ligation, or in an emulsion. This createscircles of DNA with a fragment of unknown DNA and a joined linkercontaining two divergent TypeIIs restriction sites. These circles aredigested with the TypeIIs enzyme creating a structure of: a tag, thejoined linker, another tag. These tags come from the 5′ and 3′ ends ofthe prepared DNA fragment. These tags are purified from a gel and can,optionally, be concatemerized to form DNA strands containing numerouspaired tags. In an alternative method, the tags are purified and can besequence in parallel on a large scale. The concatemerized tags caneither be cloned directly, or amplified using the Polymerase ChainReaction (PCR) amplification with Phi29 or similar polymerases prior tocloning. Tags and their paring information are decoded using DNAsequencing.

In a second method, a linker containing a portion of a TypeIIsrestriction followed by a non-compatible restriction site such as BstXIsite, is ligated onto either end of the prepared DNA fragments. Excesslinker is removed using a purification method such as gel purification,solid phase immobilization, solid phase reversible immobilization(SPRI), filtration, or selective precipitation. The DNA fragments withlinkers attached are ligated to an adapter/vector which comprises acompatible form of the BstXI or similar site, the remainder of theTypeIIs site with internal divergent primer sites at a molarity thatencourages circularization of the DNA on the vector/adapter. The circlesare selected on a gel and digested with the TypeIIs restriction sitecreating linear fragments with structure: a tag, the adapter/vector,followed by another tag. These tags come from the 5′ and 3′ ends of theprepared DNA fragment and are blunted using appropriate enzymes prior tothe subsequent ligation. The structure is ligated at a low molarity toencourage high intramolecular ligation rather than intermolecularligation, or alternatively, in an emulsion under conditions that favorligation of a single adapter/vector to a single prepared genomicfragment. The circles that are formed contain primer sites outside ofthe ligated tag pair. These primer sites are used to amplify the pairedtags plus flanking sites. The amplification product is digested with therare cut site and the tag pair purified, or the flanking sites removedusing streptavidin purification if the primers were labeled with biotin.The purified tag pairs are concatemerized and cloned. Tag pairinformation is obtained by sequencing of the concatemers.

EXAMPLE 3 Paired Tag Two-Hybrid

This method provides a linked pair of bait and prey molecules thatderive from cells that screen positive for an interaction. The bait-preypairs can be sequenced individually, for example, from plasmids, PCR orrolling circle amplification (RCA) products, or from short sequencepaired tags. The paired tags can be catenated into longer molecules andsequenced using conventional unidirectional or paired end sequencingmethods to generate approximately a 6-10 tag pair sequences from eachsequencing read. The linking of bait and prey tags allows thousands ofbaits to be screened against thousands of preys (e.g., completelibraries of both) simultaneously in a single transformation andscreening experiment. The catenation of tag pairs allows approximately10 or more pairs to be characterized for the cost of one hi-copy plasmidsequencing read (depending on the read length). By using a paired endsequencing approach, approximately 12-20 tag pairs can be generated fromeach plasmid template isolated.

The principle of the method illustrated below for the bacterialtwo-hybrid system (Dove and Hochschild, Genes and Development12:745-754, 1998) in FIG. 5. Clone libraries containing the bait andprey ORFs are typically generated in the pBT and pTRG plasmids accordingto established methods (for example, the ORFs can be prescreened bysequencing to select a genomic subset representing only the particularORFs, sub-ORFs or domains of interest). The pBT and pTRG plasmids can bemodified to contain a loxP or other phage attachment site at the cloningsites where ORFs are inserted. The cloning site modification may alsocontain, for example, a type-IIs restriction endonuclease cleavage site(such as Mmel) in such an orientation that restriction digestion willresult in the generation of a short tag sequence adjacent to the loxP orother phage attachment site. Another modification includes arare-cutting restriction endonuclease site to allow excision of the loxPsite from the recombined product (described below). Cells containingindividual bait plasmids are transformed with prey plasmids, oralternatively the prey molecules are introduced into cells byconjugation or by phage infection. The reciprocal experiment can also beperformed (for example., transforming cells containing prey plasmidswith a bait library). The cells into which the constructs aretransferred can additionally contain an inducible Cre recombinase orother phage integrase gene in addition to the appropriate geneticcomponents for the two-hybrid screening. The presence of interactingbait and prey pairs are detected, for example, by selection on agarplates containing ampicillin or carbenicillin using techniques that arestandard in the art. Expression of the recombinase is induced in theselected cells to allow recombination between the two plasmids. If twodifferent mutant loxP sites are used (e.g., lox71 and lox66) on the baitand prey constructs, respectively, then a unidirectional recombinationevent can be induced upon Cre expression (see Albert, et al., Plant J.7:649-59, 1995, and Zhang and Lutz, Nucleic Acids Research 30:e90,2002). This will increase the efficiency of generation of the recombinedproduct, pJOIN, and will ensure that the bait-prey pairs do not undergoany further recombination after initial formation (because the lox sitebetween them will be a double mutant). While this is advantageous, it isnot absolutely required for the successful practice of the method.

After recombination, the pJOIN plasmid can be isolated by standardmethods, or the bait-prey pair can be amplified, for example, by PCRusing primers flanking the 3′ ends of the bait and prey genes. The baitand prey ORFs can be identified, for example, by complete sequencing, orby primer-directed sequencing outward from the loxP site (or formanother sequence introduced into the starting plasmids flanking the loxPsites, e.g., an M13 sequencing primer binding site).

Alternatively, plasmid DNA can be prepared from a large pool of selectedcolonies and digested with MmeI (or another distally-cleavingrestriction endonuclease, such as a type-Ius enzyme) to releaseapproximately 85 bp fragments containing the loxp site flanked by baitand prey tags. Alternatively, the pooled plasmid molecules can be cut ata pair of rare-cutting endonuclease sites (e.g., AsiSI) flanking themutant loxP site between the bait and prey ORFs and the plasmids can berecircularized to eliminate that loxP site prior to MmeI digestion. Thiswill remove the approximately 34 bp lox site, resulting in approximately56 bp fragments after MmeI digestion, which can be purified, forexample, by gel electrophoresis. A linker with appropriate overhangingends (e.g., two base 3′ overhangs of random sequence to match the MmeIends) is ligated to the purified fragments (this preserves the full taglength of 20 bp). Digestion of the ligated linkers at a rare-cuttingrestriction endonuclease recognition site contained within them (e.g.,Ascl) will result in compatible termini on all of the fragments allowingthem to be ligated together (for example, after a suitable purificationstep to remove excess linkers and linker fragments) to form aconcatemer. After catenation of the fragments, the DNA can befragmented, for example, sheared or subjected to shearing, or to partialdigestion with AscI to generate fragments of approximately 1.5-2 kb insize. These fragments are typically cloned into high copy numbervectors, such as pSMART or pUC for sequencing. Sequencing of the tagpairs is accomplished by standard methods.

The method herein described is illustrated in conjunction with thebacterial two-hybrid system. However, it can also be used in conjunctionwith yeast two-hybrid screening using the appropriate vectors. TheCre/loxP recombination system (or other site-specific recombinationsystem can be used as will be understood by one of skill in the art) canbe used with inducible expression of the heterologous Cre recombinase inthe appropriate yeast host. In one method, to improve the recovery oflarge amounts of plasmid from yeast cells, the plasmids can be amplifiedby passage through E. coli, or by rolling circle amplification.Alternatively, the region including the bait-prey tags can be amplifiedby PCR using primers that hybridize outside of the cloned ORF sequences(e.g., in the fused genes, promoter regions or multiple cloning sites).

The tagging method generates paired tags from bait and prey moleculesthat originally existed on different plasmids that were introduced intothe target cells at different times. Paired tag formation can also beaccomplished by cloning bait and prey molecules into a modifiedtwo-hybrid vector in which the two ORFs are appropriately arranged in asingle vector with relation to the distally-cleaving restriction enzyme,such as MmeI or other type-Ius restriction sites, so that theintervening regions are excised enzymatically. This permits thebait-prey paired tags to be generated without using recombination.

EXAMPLE 4 Method for Generating Paired Genome Sequence Tags

Detecting genome amplifications, deletions and translocations has beenshown to pinpoint genes of interest in various disease states includingcancer and mental retardation. Paired-end sequences have been showncapable of detecting these regions of change in previously sequencedgenomes in addition to improving the assembly of novel shotgunsequences. In this method of “Digital Karyotyping,” translocations,amplifications and deletions can be detected in a previously sequencedgenome using “Paired Genome Sequence Tags” (PGSTs). These tags can beproduced, for example, using a Type IIs restriction enzyme similar tothose generated in Digital Karyotyping and SAGE. The tags in PGST,however, are generated from both ends of DNA fragments and remainassociated through concatemerization and sequencing steps. This producespaired tags a defined distance from each other in the genome. Greaterthan about 15 tag pairs can be obtained from a single sequence. The tagscan be used to detect regions of amplification and deletion inpreviously sequenced genomes. The additional information obtainedthrough pairing also allows the detection of translocations. This methodalso applies to generating paired tag information for scaffolding genomeshotgun assemblies. In this method, paired-end sequence information isproduced in an extremely efficient manner that is free from cloningbiases and is a valuable method in genome shotgun sequencing.

Creation of a PGST Linker

An oligonucleotide and its complement containing two BstXI restrictionrecognition sites separated by an RsaI recognition site weresynthesized. The oligonucleotide has the sequence:AGCTTCCATGGATTTGGAGTACACCAAATCCATGGT (SEQ ID NO:2)In this example, the BstXI sites were designed to have the samerecognition site sequence and which were not complementary to each otherso that cleavage with BstXI would not generate a 5′ and 3′ end whichcould self-ligate. Furthermore, the oligonucleotide and its complementwere designed to contain one nucleotide base of a Type Ius restrictionenzyme recognition site, in this example, MmeI, as well as a portion ofan additional restriction enzyme recognition site, in this case BamHI,which was used later for concatenation of the paired genome sequencetags (also referred to herein as paired tags).

The oligonucleotide and its complement were annealed to produce a doublestranded oligonucleotide which was inserted into a vector, such as pUC18 or pUC 19, between an M13R primer site/SP6 promoter and an T7promoter/M13F primer site. The vector was digested with the restrictionenzyme PvuII, which has two recognition sites that flank the M13R primersite/SP6 promoter and T7 promoter/M13F primer sites, to release afragment having the order:

-   -   --PvuII-M13R/Sp6-BstXI-RsaI-BstXI-T7/M13F-PvuII--        This fragment was purified using agarose gel electrophoresis and        the fragment circularized on itself by intramolecular ligation.        The circularized fragment was then digested with the restriction        enzyme RsaI to create a linear linker having the order:    -   --BstXI-Sp6/M13R-PvuII-M13F/T7-BstXI--        This linker was inserted by blunt end cloning into an E.        coli-based vector (such as the pAGEN vector) which did not        contain any of the primer sites contained in the above linker.        The linker construct was transformed into an E. coli strain for        maintenance, propagation and amplification of the linker, using        standard protocols as will be understood by one of skill in the        art.        Preparation of the Linker for Use in the System

A plasmid DNA preparation from the strain containing the linkerconstruct was digested with the restriction enzyme BstXI, therebyreleasing the linker and creating identical, non-complementary, 3′overhangs on either side of the linker.

Preparation of DNA of Interest for Ligation to the Linker

The nucleic acid sequence or DNA of interest, in this example, the E.coli genome, was sheared using a mechanical method (either nebulization,hydrodynamic shearing through a small orifice, or sonication). Therandomly sheared DNA was end repaired using nucleotides (dNTPs) with T4DNA Polymerase which has 5′-3′ polymerase activity as well as 3′-5′exonuclease activity which fills in 3′ overhangs and cuts back 5′overhangs, respectively. In this example, the T4 DNA Polymerase with thefree nucleotides (dNTPs) filled in the BstXI 3′ overhangs. Thisend-repaired randomly sheared DNA was separated by size using agarosegel electrophoresis. Fragments of the desired size, in this example, 2-3kilobases (kb), were cut from the gel and purified using standard gelpurification columns. The purified, size selected DNA fragments wereligated to specific DNA adaptors in vast molar excess to ensure that theDNA fragments neither circularized nor ligated to the end of another DNAfragment. The DNA adaptors were complementary to the digested BstXIsites of the linker prepared earlier. The adapter has the following topand bottom strands: (top strand)     5′ CCGACA 3′ (SEQ ID NO:3)       |||||| (bottom strand) 3′ CCTAGGCTGT 5′ (SEQ ID NO:4)The blunt end of the adapter is ligated to the fragment of interestwhile the overhang is complementary to the overhang left after digestionof the DNA linker with BstXI. Excess adapter was removed by agarose gelpurification of the 2-3 kb adapted DNA fragments.Ligation of the Adapted DNA Fragments to the Linker

The adapted DNA fragments were ligated to the DNA linker (preparedabove) using the following formulas to determine the molar ratio ofadapted DNA fragments to DNA linker to ensure the greatest number ofcircular fragments comprising one adapted DNA fragment and one DNAlinker generated by intramolecular interactions during ligation (CurrentProtocols in Human Genetics (1994) “Construction of Chromosome Jumpingand Linking Libraries in E. coli” by Drumm, Eds. Nicholas C. Dracoploiet al.):J=K/S ^(1/2)N=J/(I+J)Where, K is the constant 63.4 micrograms per milliliter (μg/mL), S isthe size of the DNA fragment ligated to the linker in units of Kilobases(kb), N is the fraction of intramolecular interactions (e.g., 0.95=95%intramolecular interactions), and I is the concentration of DNA inmicrograms per milliliter (μg/mL) to obtain the desired fraction ofintramolecular interactions.

Ligation of the DNA linker to the adapted DNA fragments creates a fullMmeI site and a full BamHI site on either end of the adapted DNAfragment due to the design of the linker and the adapter. The circularDNA was purified from the other products of the ligation reaction bysize separation on an agarose gel. The circular DNA was digested withMmeI releasing all of the DNA fragment except a 20/18 bp tag on eitherside of the DNA linker (i.e., a paired tag on the linker). The 20 bp isthe number of nucleotides remaining from the restriction endonucleaserecognition site in the 5 prime to 3 prime direction of the DNA upondigestion with the restriction enzyme. Likewise, the 18 bp refers to thenumber of nucleotides remaining from the enzyme recognition site on the3 prime to 5 prime strand upon digestion with the restriction enzyme.

The DNA linker plus the paired tags from the DNA fragment of interestwere separated from other digestion fragments by size selection usingagarose gel electrophoresis using standard protocols. The DNA linkerplus the paired tags were blunt ended to remove the 3′ overhang using T4DNA Polymerase to leave 18 bp of each of tag in the paired tag. The DNAlinker plus blunt-ended paired tag was subsequently purified usingphenol/chloroform extraction. Each DNA linker plus the blunt-endedpaired tags were self-ligated to form a circular DNA using the aboveformula to ensure intramolecular interactions leading to formation ofsingle circles such that the paired tags were now adjacent to eachother. This circularization also caused the primer sites (M13R/Sp6 andT7/M13F) on the DNA linker flanking the paired tags to become convergent(i.e., while the DNA linker is linear, the PCR primer sites are directedaway from each other (divergent), but upon circularization, the primersites are directed toward each other thereby allowing amplification ofthe intervening DNA (the paired tags).

Using the primer sites, the joined paired tags were PCR amplified usingstandard PCR conditions, gel purified, and digested with BamHI torelease the joined paired tags flanked by cut BamHI sites. The releasedjoined paired tags flanked by cut BamHI sites were gel purified usingPolyAcrylamide Gel Electrophoresis (PAGE) followed by elution of thepaired tags from the gel. The released paired tags flanked by cut BamHIsites (“sticky ends”) were concatenated by ligation to each other viathe BamHI sticky ends to form concatemers of approximately 600-800 basepairs. The concatemers were size-selected on an agarose gel andsubsequently purified. The purified, size-selected concatemers wereligated into the BamHI site of pUC-based E. coli vector (e.g., pUC18),and the construct transformed into E. coli using standardelectroporation procedures. Colonies containing the concatemer vectorswere selected, grown, and plasmid DNA was prepared from them forsequencing using standard protocols.

The plasmid DNA was sequenced using cycle sequencing kits from AppliedBiosystems and separated on an Applied Biosystems 3730XL DNA analyzer.The readout sequences were then separated using a PERL script whichsplit the sequences based on the flanking BamHI sites in order toidentify the sequences of the paired tags. Individual tags in the pairedtag were determined by using the substring of sequence on each side of apaired tag that contained the BamHI recognition site plus 18nucleotides. The BamHI restriction site was subtracted from the tagsequence and the tag sequence matched to a hash of all 18mers in the E.coli genome. As will be understood by a person of skill in the art, a“hash” is a standard computing term meaning an array of arrays, or alist of lists in which the first list contains each 18mer in the genomeas separate entries and each 18mer entry has associated with it a listof information, which in this case has information regarding where the18 mer is located in the genome and which strand it was located. Thehash of all 18 mers in the E. coli genome contained information on thelocation and orientation of each 18 mer present in the genome. Each tagwas therefore assigned a location and orientation in the genome. Sometags matched repetitive 18 mers in the genome, i.e., a stretch of 18nucleotides was found in multiple locations in the genome. In thesecases, half of the repetitive 18 mer tags sequenced were unambiguouslyplaced based on the location and orientation of their paired tag mate.Initial analysis of 45 unique paired tags obtained from the sequencingrevealed approximately 85% of them were correctly paired, i.e., thepaired tag sequences were both the expected 2-3 kb distance away fromeach other and on opposite strands in the genome.

EXAMPLE 5 Method for Generating Paired Genome Sequence Tags

This method generates paired tags from the ends of a set of genomic DNAfragments by generating the tags by fragmentation means other than bycleavage with restriction endonucleases that cleave distally to theirrecognition sites. This method produces end-sequence tags in which thetag length can be arbitrarily large, thus accommodating longer sequenceread lengths than the shorter sequence read lengths (e.g., 18-27 bases)typically obtained by a restriction endonuclease approach.

This method is particularly useful for generating DNA sequenceinformation from each of the two ends of a set of DNA fragments in sucha way that the pairing information is preserved. Such information isuseful for de novo sequencing and DNA sequence assembly using genomeassembly software such as Arachne, the Paracel Genome assembler, Jazz orthe Celera Assembler. It is also useful for re-sequencing, polymorphismdiscovery and genotyping applications to characterize the geneticdifferences between genomes from different individuals, for example,between two human genomes, to characterize a genome for the presence ofknown mutations or polymorphisms, or to characterize associationsbetween specific sequences or polymorphisms with particular phenotypes,predisposition to disease or with other traits of interest. Anillustration of the method is presented in FIG. 9.

Some steps of this procedure are optional, or could be substituted byother specific methods. In a particular embodiment, the method comprisescircularizing a first set of DNA fragments (“1” in FIG. 9), produced byrandom fragmentation of the DNA to be sequenced (e.g., a genomic DNAsample—this could be accomplished by mechanical shearing, or byspecific- or non-specific endonuclease digestion, oxidativefragmentation by metal ions, or any other fragmentation means) using ashort DNA linker that has an attached affinity tag (3 in FIG. 9) toallow subsequent binding and recovery of DNA fragments containing theaffinity tag. The method shown in FIG. 9 specifies ligation ofnon-self-complementary end-linkers (2 in FIG. 9) having a unique 5′ or3′ overhang to the starting set of fragments prior to circularization(after healing the ends on the starting set of fragments to create bluntends using a combination of DNA polymerase(s), exonuclease(s) and/orpolynucleotide kinase). This approach improves the specificity of thesubsequent circularization step to ensure that the DNA fragments do notself-ligate or circularize without incorporating the affinity tag linker(3 in FIG. 9), which, in the above example comprises a set ofnon-self-complementary ends that are complementary to those on theend-linkers (2 in FIG. 9). After circularization, the sample is treatedwith Bal31, (or with a similar exonuclease, or with a mixture of anexonuclease plus a single-stranded DNA specific exo- or endonuclease, orwith a commercial “plasmid-safe” DNAse product) to destroy any leftoverlinear molecules including any unligated affinity tag. The exonucleaseis inactivated, and the remaining circles are fragmented into smallerpieces to produce a second set of DNA fragments. The pieces that containthe affinity tag are captured, purified and are then sequenced: a)directly, using a single molecule sequencing approach, b) aftermolecular cloning using standard methods (e.g., after ligation into aselectable vector followed by transformation and propagation ofindividual fragments in E. coli or other suitable host), or c) afteramplification by PCR (with or without the addition of universal primingsites (4) by ligation of oligonucleotides at the ends). One method foramplification and sequencing, shown in the figure above, is by clonalamplification on magnetic beads containing an oligonucleotidecomplementary to the universal primers (4 in FIG. 9) in a water/oilemulsion (or by some other clonal amplification means) such that theamplified fragments become bound to the beads in both possibleorientations. Alternate means of amplifying after applying means forattachment of different primers to the two ends of the sheared fragmentscould be applied to produce magnetic beads with the final amplifiedfragments in one orientation only.

The affinity tag shown in FIG. 9 represents biotin attached to one ofthe nucleotides, but many other types of affinity tags could be used,such as digoxygenin or other small molecule for which specificantibodies are available. Alternatively, a target sequence for a DNAbinding protein such as the E. coli lactose repressor could be includedin the linker, or a sequence capable of being hybridized as a triplehelix. In the example above, the DNA fragments would be recovered bybinding to a matrix (e.g., magnetic beads) with immobilized streptavidinprior to ligation of the universal primer oligonucleotides

The affinity tag oligonucleotide comprises sequences that double assequencing primers. A different primer is used to sequence in eachdirection outward from the tag.

An advantage of this method over previous methods is that it cangenerate tags of any desired length, up to several kilobases, onaverage, if desired. Paired tag fragment lengths of several hundredbases would be adequate to support sequence read lengths of 25-200 basesusing conventional Sanger sequencing or revolutionary sequencing bysynthesis methodologies, such as Polony Technology as developed by G.Chuch and colleagues, Pyrosequencing in picotiter plates as developed by454 corporation, or Massively Parallel Signature Sequencing as developedby Lynx Therapeutics. The precise size of the two sub-fragments flankingthe affinity tag linker will be variable, and unknown, but on average itwill be about half of the total fragment length). Thus for a 50 baseread length and a total fragment length of 580 bases with a 30 baseaffinity tag, 90% of sequence reads originating from the affinity tagwould be at least 50 bases long. If longer read lengths are desired, alonger paired tag fragment length can be generated.

One means for attachment of two different primers to the two ends of thefinal fragments involves the use of a second circularization step tointroduce two different sequences capable of being used as PCR primersinstead of ligating a single universal primer. The advantage of thisimplementation is that it avoid the requirement for doing PCR on asupport using a single primer by “bridge PCR”—a method that is known toresult in poor efficiency of fragment amplification and which alsoresults in both DNA strands being attached to the support, which reducessequencing efficiency. The second circularization method is illustratedin the lower half of FIG. 10.

The first steps in this procedure are the same as before. A first set ofDNA fragments (1 in FIG. 10) produced by fragmentation of genomic DNAare circularized using a short DNA linker that has an attached affinitytag (3 in FIG. 10) to allow subsequent binding and recovery of DNAfragments containing the affinity tag. As, before, the method employsinitial ligation of non-self-complementary end-linkers (2 in FIG. 10)having a unique 5′ or 3′ overhang to the starting set of fragments priorto circularization (after healing the ends on the starting set offragments to create blunt ends using a combination of DNA polymerase(s),exonuclease(s) and/or polynucleotide kinase). The capping step improvesthe specificity of the subsequent circularization step to ensure thatthe DNA fragments do not self-ligate or circularize withoutincorporating the affinity tag linker (3 in FIG. 10), which, in theabove example comprises a set of non-self-complementary ends that arecomplementary to those on the end-linkers (2 in FIG. 10). The length ofthe affinity tag linker is at least 20 nucleotides, such that two uniqueprimer sequences (A and B) can be accommodated, which will allowhybridization of primers to both DNA strands to allow priming of DNAsynthesis in either direction, as seen in FIG. 11.

After circularization, the sample is treated with Bal31, (or with asimilar exonuclease, or with a mixture of an exonuclease plus asingle-stranded DNA specific exo- or endonuclease, or with a commercial“plasmid-safe” DNAse product) to destroy any leftover linear moleculesincluding any unligated affinity tag. The endonuclease is inactivatedand the remaining circles are fragmented into smaller pieces to producea second set of DNA fragments. The pieces that contain the affinity tagare captured at this point, by mixing with streptavidin coated magneticbeads, for example. After healing the ends on the starting set offragments to create blunt ends using a combination of DNA polymerase(s),exonuclease(s) and/or polynucleotide kinase), a capping linker (2 inFIG. 11) is added to the linear DNA fragments. As before, the preferredcapping linker has non-self-complementary ends with a unique 5′ or 3′overhang. This approach improves the specificity of the subsequentcircularization step to ensure that the DNA fragments do not self-ligateor circularize without incorporating the inversion linker (4 in FIG.11), which, in the above example comprises a set ofnon-self-complementary ends that are complementary to those on theend-linkers (2 in FIG. 11). The inversion linker (4 in FIG. 11)comprises two unique sequences (C and D) that can be used subsequentlyto prime DNA synthesis in a PCR reaction, and a rare-cuttingendonuclease site between the C and D sequences. After circularization,the sample is treated with Bal31, (or with a similar exonuclease, orwith a mixture of an exonuclease plus a single-stranded DNA specificexo- or endonuclease, or with a commercial “plasmid-safe” DNAse product)to destroy any leftover linear molecules including any unligatedinversion tag. The nuclease is inactivated and the remaining circles arelinearized using the rare-cutting Endonuclease (or other rare cleavagemeans), in the case illustrated the endonuclease is I-Scel. If desired,a second round of enrichment for fragments containing the affinity tagcould be performed at this stage.

As before, sequencing could be done: a) directly, using a singlemolecule sequencing approach, b) after molecular cloning using standardSanger methods (e.g., after ligation into a selectable vector followedby transformation and propagation of individual fragments in E. coli orother suitable host), c) after amplification by PCR, or d) after clonalamplification using polony technology, emulsion PCR, bridge PCR, or someother clonal amplification means. A preferred method for amplificationand sequencing is by clonal amplification on magnetic beads containingan oligonucleotide complementary to one end of the molecules to beamplified (in a water/oil emulsion, for example) such that the amplifiedfragments become bound to the beads in only one orientation. Forexample, if the “C” primer is covalently attached to the beads through achemical linker at the 5′ end (or non-covalently using 5′ biotin andstreptavidin beads—or by some other high affinity non-covalentattachment means). Molecules amplified on beads will then becomeattached as shown in FIG. 12.

All molecules on any one bead will contain the same sequences, in thesame orientation. The unattached strand can then be removed bydenaturation. On some beads (I. in FIG. 12), the orientation of theaffinity-tag linker will be such that a primer complementary to the Asequence will hybridize to attached DNA strand. On other beads (II. inFIG. 12), the orientation of the affinity-tag linker will be such that aprimer complementary to the B sequence will hybridize to attached DNAstrand. By performing a sequencing by synthesis procedure on a mixtureof clonally amplified templates (e.g., a mixture of beads on a polonyslide) sequentially with two sets of primers, sequences from both endsof the starting set of DNA fragments (1 in FIG. 12) can be acquired. Todo this, sequences are first generated by priming with the D primer(each bead with clonally amplified molecules will produce a uniquesequence). Next, sequences are generated by priming with a mixture ofthe A and B primers (each bead with clonally amplified molecules willproduce a unique sequence, primed from either the A or B primer only).

The starting set of fragments (1 in FIG. 12) can be of any length up toseveral hundred kilobases, but preferably will be in the range of 2 to200 kb. The second set of DNA fragments (produced after circularizationwith the affinity tag) can be of any length up to the size of the firstset of fragments, but preferably will be in the range of 0.1 to 2 kb.The average read length that can be obtained from each end will be equalto ½ the length of the second set of fragments minus the length of theaffinity tag linker.

The relevant teachings of all the references, patents and patentapplications cited herein are incorporated herein by reference in theirentirety.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method for producing a paired tag from a first nucleic acidsequence fragment, without cloning, comprising the steps of: a) joiningthe 5′ and 3′ ends of a first nucleic acid sequence fragment via a firstlinker such that the first linker is located between the 5′ end and the3′ end of the first nucleic acid sequence fragment in a circular nucleicacid molecule; b) cleaving the circular nucleic acid molecule, therebyproducing a second nucleic acid fragment comprising paired tag wherein a5′end tag of the first nucleic acid sequence fragment is joined to a 3′end tag of the first nucleic acid sequence fragment via the firstlinker.
 2. The method of claim 1, wherein: a) the linker comprises atleast two restriction endonuclease recognition sites specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site; and b) thecircular nucleic acid molecule is cleaved with a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site to thereby producing thepaired tag.
 3. (canceled)
 4. The method of claim 1 wherein step a)comprises the steps of: a) joining the 5′ and 3′ends of a first nucleicacid sequence fragment to at least one adapter; b) cleaving theadapter(s), thereby producing a second nucleic acid sequence fragmentwith compatible ends; and c) circularizing the second nucleic acidsequence fragment such that a 5′end of the first nucleic acid sequencefragment is joined to a 3′ end of the first nucleic acid sequencefragment via a first linker derived from the adapter(s), therebyproducing a circular nucleic acid molecule.
 5. The method of claim 4,wherein: a) the adapter comprises at least two restriction endonucleaserecognition sites specific for a restriction endonuclease that cleavesthe nucleic acid sequence fragment distally to the restrictionendonuclease recognition site; b) the adapter comprises a restrictionendonuclease recognition site specific for a rare cutting restrictionendonuclease; c) cleaving the adapter joined to the nucleic acidsequence fragment with a rare cutting restriction endonuclease toproduce the compatible ends; and d) cleaving the circular nucleic acidmolecule with a restriction endonuclease that cleaves distally to therestriction endonuclease recognition site.
 6. (canceled)
 7. The methodof claim 1 further comprising the steps of: c) joining a second linkerto the 5′ and 3′ ends of the second nucleic acid sequence fragment; andd) amplifying the second nucleic acid fragment using an oligonucleotidecomplementary to a sequence present in the second linker.
 8. The methodof claim 1 further comprising the steps of: c) joining the 5′ and 3′ends of a second nucleic acid sequence fragment via a second linker suchthat the second linker is located between the 5′ end and the 3′ end ofthe second nucleic acid sequence fragment in a second circular nucleicacid molecule; and d) amplifying a nucleic acid sequence fragment fromthe second circular nucleic acid molecule using two oligonucleotidescomplementary to sequences present in the second linker.
 9. The methodof claim 8, wherein the second linker comprises a recognition site for arare-cutting restriction endonuclease, and the second circular nucleicacid molecule is cleaved using a rare-cutting restriction endonucleasethat recognizes the site in the second linker.
 10. The method of claim7, wherein: a) the first linker comprises at least two restrictionendonuclease recognition sites specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site; and b) the first circularnucleic acid molecule is cleaved with a restriction endonuclease thatcleaves the nucleic acid sequence fragment distally to the restrictionendonuclease recognition site. 11-12. (canceled)
 13. The method of claim12, wherein the second nucleic acid fragment is purified by affinitycapture using a reagent specific for the first linker prior toamplification, wherein the reagent is selected from the group consistingof biotin a sequence capable of forming a triple helix and a recognitionsite for a DNA binding protein. 14-16. (canceled)
 17. A method forcharacterizing a paired tag from a first nucleic acid sequence fragment,without cloning, comprising the steps of: a) joining the 5′ and 3′ endsof a first nucleic acid sequence fragment to a linker such that thelinker is located between the 5′ end and the 3′ end of the first nucleicacid sequence fragment in a circular nucleic acid molecule; b) cleavingthe circular nucleic acid molecule, thereby producing a second nucleicacid sequence fragment wherein a 5′end tag of the first nucleic acidsequence fragment is joined to a 3′ end tag of the first nucleic acidsequence fragment via the linker; c) amplifying the second nucleic acidfragment; and d) characterizing the 5′ and 3′end tags of the amplifiedsecond nucleic acid fragments.
 18. A method for characterizing a nucleicacid sequence, without cloning, comprising the steps of: a) fragmentinga nucleic acid sequence thereby producing a plurality of first nucleicacid sequence fragments having a 5′ end and a 3′ end; b) joining the 5′and 3′ ends of each first nucleic acid sequence fragment to a firstlinker such that the first linker is located between the 5′ end and the3′ end of each first nucleic acid sequence fragment in a circularnucleic acid molecule; c) cleaving the circular nucleic acid molecules,thereby producing a plurality of second nucleic acid sequence fragmentswherein a subset of the fragments comprise a paired tag derived fromeach first nucleic acid sequence fragment joined via the first linker;d) joining a second linker to the 5′ and 3′ ends of the second nucleicacid sequence fragments; e) amplifying the second nucleic acid fragmentsusing an oligonucleotide complementary to a sequence present in thesecond linker; and f) characterizing the 5′ and 3′end tags of theamplified second nucleic acid fragments.
 19. A method for characterizinga nucleic acid sequence, without cloning, comprising the steps of: a)fragmenting a nucleic acid sequence thereby producing a plurality offirst nucleic acid sequence fragments having a 5′ end and a 3′ end; b)joining the 5′ and 3′ ends of each first nucleic acid sequence fragmentto a first linker such that the first linker is located between the 5′end and the 3′ end of each first nucleic acid sequence fragment in acircular nucleic acid molecule; c) cleaving the circular nucleic acidmolecules, thereby producing a plurality of second nucleic acid sequencefragments wherein a subset of the fragments comprise a paired tagderived from each first nucleic acid sequence fragment joined via thefirst linker; d) joining the 5′ and 3′ ends of each second nucleic acidsequence fragment via a second linker such that the second linker islocated between the ends of each second nucleic acid sequence fragmentto form a plurality of second circular nucleic acid molecules; e)amplifying the second circular nucleic acid molecules twooligonucleotides complementary to sequences present in the secondlinker, thereby producing a plurality of amplified nucleic acidfragments; and f) characterizing the 5′ and 3′end tags of the pluralityof amplified nucleic acid fragments.
 20. A method for characterizing anucleic acid sequence, without cloning, comprising the steps of: a)fragmenting a nucleic acid sequence thereby producing a plurality offirst nucleic acid sequence fragments having a 5′ end and a 3′ end; b)joining the 5′ and 3′ ends of each first nucleic acid sequence fragmentto a first linker such that the first linker is located between the 5′end and the 3′ end of each first nucleic acid sequence fragment in acircular nucleic acid molecule; c) cleaving the circular nucleic acidmolecules, thereby producing a plurality of second nucleic acid sequencefragments wherein a subset of the fragments comprise a paired tagderived from each first nucleic acid sequence fragment joined via thefirst linker; d) joining the 5′ and 3′ ends of each second nucleic acidsequence fragment via a second linker such that the second linker islocated between the ends of each second nucleic acid sequence fragmentto form a plurality of second circular nucleic acid molecules; e)cleaving the second circular nucleic acid molecules; f) amplifying thecleaved second circular nucleic acid molecules using twooligonucleotides complementary to sequences present in the second linkeras PCR primers thereby producing a plurality of amplified nucleic acidfragments; and g) characterizing the 5′ and 3′end tags of the pluralityof amplified nucleic acid fragments.
 21. The method of claim 20, whereinthe second linker comprises a recognition site for a rare-cuttingrestriction endonuclease, and the second circular nucleic acid moleculeis cleaved using a rare-cutting restriction endonuclease that recognizesthe recognition site for a rare-cutting restriction endonuclease in thesecond linker.
 22. The method of claim 20, wherein the second circularnucleic acid molecules are cleaved non specifically.
 23. The method ofclaim 17, wherein: a) the first linker comprises at least tworestriction endonuclease recognition sites specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site; b) the first circularnucleic acid molecules are cleaved with a restriction endonuclease thatcleaves the nucleic acid sequence fragment distally to the restrictionendonuclease recognition site.
 24. The method of claim 10, wherein therestriction endonuclease recognition sites specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site are immediately adjacentto the ends of the first nucleic acid sequence fragments.
 25. (canceled)26. The method of claim 19, wherein the second nucleic acid fragment ispurified from other nucleic acid fragments by affinity capture using areagent specific for the first linker prior to amplification, whereinsaid reagent is selected from the group consisting of biotin a sequencecapable of forming a triple helix and a recognition site for a DNAbinding protein. 27-29. (canceled)
 30. The method of claim 20, whereinthe nucleic acid sequence is a genome.
 31. The method of claim 30,wherein the method karyotypes or sequences the genome.
 32. (canceled)33. A composition comprising nucleic acid sequence elements arranged inthe following order: linker 1--5′end tag--linker 2--3′end tag--linker 3wherein the 5′end tag and the 3′end tag comprise a paired tag derivedfrom a single contiguous nucleic acid sequence fragment.
 34. (canceled)35. The composition of claim 33, wherein linker 2 comprises: a) at leasttwo restriction endonuclease recognition sites specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site, and isoriented in such a way that one of the sites directs cleavage within the5′end tag or at the junction of linker 1 and the 5′end tag, and theother site directs cleavage within the 3′ end tag or at the junction oflinker 3 and the 3′end tag; and/or b) at least one recognition site fora rare-cutting restriction endonuclease located between the tworestriction endonuclease recognition sites specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site.
 36. The composition ofclaim 33, wherein linker 1 and linker 3 are the same sequence in reverseorientation.
 37. The composition of claim 33, wherein the composition isamplified using oligonucleotides complementary to sequences present inlinker 1 and linker
 3. 38. The composition of claim 33, wherein linker 1and linker 3 are derived by cleavage of a circular nucleic acid moleculewith a rare-cutting restriction endonuclease comprising a recognitionsite between linker 1 and linker
 3. 39. A composition comprising acircular nucleic acid molecule, wherein sequence elements are arrangedin the following circular order:

wherein the 5′end tag and the 3′end tag comprise a paired tag derivedfrom a single contiguous nucleic acid sequence fragment.
 40. (canceled)41. The composition of claim 39, wherein linker 2 comprises: a) at leasttwo restriction endonuclease recognition sites specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site, and areoriented in such a way that one of the sites directs cleavage within the5′end tag or at the junction of the 5′end tag and linker 2 and, and theother site directs cleavage within the 3′ end tag or at the junction ofthe 3′end tag and linker 2; and/or b) at least one recognition site fora rare-cutting restriction endonuclease located between the tworestriction endonuclease recognition sites specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site.
 42. The composition ofclaim 39, wherein linker 2 is palindromic.
 43. The composition of claim39, wherein linker 2 comprises a recognition site for a rare-cuttingrestriction endonuclease.
 44. The composition of claim 39, wherein thecomposition is amplified isothermally using oligonucleotide primerscomplementary to sequences in either linker 1 or linker 2, or in bothlinker 1 and linker
 2. 45. (canceled)
 46. A method for producing apaired tag from a nucleic acid sequence, wherein the nucleic acidsequence comprises two restriction endonuclease recognition sitesspecific for a restriction endonuclease that cleaves the nucleic acidsequence distally to the restriction endonuclease recognition site,comprising the steps of: a) cleaving the restriction endonucleaserecognition sites using the restriction endonuclease that is specificfor the restriction endonuclease recognition sites, thereby producing a5′ end tag and a 3′ end tag from the nucleic acid sequence; and b)joining the 5′ end tag with the 3′ end tag from the nucleic acidsequence; thereby producing a paired tag from the nucleic acid sequence.47. The method of claim 46, wherein the nucleic acid sequence furthercomprises at least two restriction endonuclease recognition sitesspecific for a rare cutting restriction endonuclease.
 48. A method forcharacterizing a nucleic acid sequence comprising the steps of: a)fragmenting a nucleic acid sequence thereby producing a plurality ofnucleic acid sequence fragments having a 5′ end and a 3′ end; b)introducing into the 5′ end and into the 3′ end of each nucleic acidsequence fragment: (i) a restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite; and (ii) a restriction endonuclease recognition site specific fora rare cutting restriction endonuclease; thereby producing modifiednucleic acid sequence fragments; c) cleaving the restrictionendonuclease recognition site specific for a rare cutting restrictionendonuclease in each modified nucleic acid sequence fragment with therare cutting restriction endonuclease, thereby producing a plurality ofnucleic acid sequence fragments having compatible ends; d) maintainingthe fragments having compatible ends under conditions in which thecompatible ends intramolecularly ligate, thereby producing a pluralityof circularized nucleic acid sequences comprising two restrictionendonuclease recognition sites specific for restriction endonucleasesthat cleave the nucleic acid sequence fragment distally to therestriction endonuclease recognition sites; e) cleaving the circularizednucleic acid sequences at the restriction endonuclease recognition siteswith the restriction endonucleases specific for the restrictionendonuclease recognition sites, thereby producing a plurality of pairedtags comprising a 5′ end tag and a 3′ end tag of the nucleic acidsequence fragment; and f) characterizing the paired tags; therebycharacterizing the nucleic acid sequence. 49-50. (canceled)
 51. A methodfor characterizing a nucleic acid sequence comprising the steps of: a)fragmenting a nucleic acid sequence thereby producing a plurality ofnucleic acid sequence fragments having a 5′ end and a 3′ end; b)introducing into the 5′ end and into the 3′ end of each nucleic acidsequence fragment a restriction endonuclease recognition site specificfor a restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site,thereby producing a plurality of modified nucleic acid sequencefragments; c) cloning the modified nucleic acid sequence fragments,thereby producing cloned nucleic acid sequence fragments; d) cleavingthe restriction endonuclease recognition sites at the 5′ end and the 3′end of the cloned nucleic acid sequence fragments using the restrictionendonuclease that is specific for the restriction endonucleaserecognition sites, thereby producing a 5′ end tag and a 3′ end tag ofeach cloned nucleic acid sequence fragment; e) joining the 5′ end tag tothe 3′ end tag of each cloned nucleic acid sequence fragment therebyproducing a plurality of paired tags; and f) characterizing the pairedtags; thereby characterizing the nucleic acid sequence.
 52. The methodof claim 51, wherein step b) comprises step c).
 53. A method foridentifying nucleic acid sequences that encode at least two interactingproteins comprising the steps of: a) combining: (i) a first vectorcomprising: (1) a nucleic acid sequence that encodes a first proteinthat interacts with a second protein; and (2) a first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site; and (ii) a second vectorcomprising: (1) a nucleic acid sequence that encodes the second protein;and (2) a second restriction endonuclease recognition site specific fora restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site;thereby producing a combination; b) maintaining the combination underconditions in which the first protein and the second protein areexpressed and interact; c) joining the first vector with the secondvector, thereby forming a contiguous nucleic acid sequence thatcomprises: (i) the nucleic acid sequence that encodes a first proteinthat interacts with a second protein; (ii) the first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site; (iii) the nucleic acidsequence that encodes the second protein; and (iv) the secondrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site; d) cleaving the firstrestriction endonuclease recognition site and the second restrictionendonuclease recognition site in the contiguous nucleic acid sequencewith restriction endonucleases that cleave the contiguous nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a paired tag comprising 5′ end tag and a 3′ end tag ofthe contiguous nucleic acid sequence; and e) sequencing the paired tag,thereby identifying nucleic acid sequences that encode at least twointeracting proteins.
 54. A method for identifying nucleic acidsequences that encode at least two interacting proteins comprising thesteps of: a) combining: (i) a first vector comprising: (1) a nucleicacid sequence that encodes a first protein that interacts with a secondprotein; and (2) a first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite; and (ii) a second vector comprising: (1) a nucleic acid sequencethat encodes the second protein; and (2) a second restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site; thereby producing acombination; b) maintaining the combination under conditions in whichthe first protein and the second protein are expressed and interact; c)joining the first vector with the second vector, thereby forming acontiguous nucleic acid sequence that comprises: (i) the nucleic acidsequence that encodes a first protein that interacts with a secondprotein; (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite; (iii) the nucleic acid sequence that encodes the second protein;and (iv) the second restriction endonuclease recognition site specificfor a restriction endonuclease that cleaves the nucleic acid sequencefragment distally to the restriction endonuclease recognition site; d)sequencing the contiguous nucleic acid sequence; thereby identifyingnucleic acid sequences that encode at least two interacting proteins.55. The method of claim 53, wherein the method, after step d) and beforestep e), further comprises the step of: d′) joining the 5′ end tag tothe 3′ end tag, thereby producing a paired tag.
 56. The method of claim55, wherein the method identifies a plurality of nucleic acid sequencesthat encode at least two interacting proteins, the method comprising aplurality of first vectors and a plurality of second vectors, whereinthe method further comprises the step of: d″) joining the paired tags.57. A method for identifying nucleic acid sequences that encode at leasttwo interacting proteins comprising the steps of: a) combining: (i) afirst vector comprising: (1) a nucleic acid sequence that encodes afirst protein that interacts with a second protein; (2) a firstrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site; and (3) a secondrestriction endonuclease recognition site; and (ii) a second vectorcomprising: (1) a nucleic acid sequence that encodes the second protein;(2) a third restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site; and (3) afourth restriction endonuclease recognition site; thereby producing acombination; b) maintaining the combination under conditions in whichthe first protein and the second protein are expressed and interact; c)joining the first vector with the second vector, thereby forming acontiguous nucleic acid sequence that comprises: (i) the nucleic acidsequence that encodes a first protein that interacts with a secondprotein; (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite; (iii) the second restriction endonuclease recognition site; (iv)the nucleic acid sequence that encodes the second protein; (v) the thirdrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site; and (vi) the fourthrestriction endonuclease recognition site; d) cleaving the secondrestriction endonuclease recognition site and the fourth restrictionendonuclease recognition site in the contiguous nucleic acid sequencewith restriction endonucleases thereby producing compatible ends in thecontiguous nucleic acid sequence; e) maintaining the contiguous nucleicacid sequence under conditions in which the compatible ends in thecontiguous nucleic acid sequence intramolecularly ligate, therebyproducing a circularized nucleic acid sequence; and f) sequencing thecircularized nucleic acid sequence; thereby identifying nucleic acidsequences that encode at least two interacting proteins.
 58. A methodfor identifying nucleic acid sequences that encode at least twointeracting proteins comprising the steps of: a) combining: (i) a firstvector comprising: (1) a nucleic acid sequence that encodes a firstprotein that interacts with a second protein; (2) a first restrictionendonuclease recognition site specific for a restriction endonucleasethat cleaves the nucleic acid sequence fragment distally to therestriction endonuclease recognition site; and (3) a second restrictionendonuclease recognition site; and (ii) a second vector comprising: (1)a nucleic acid sequence that encodes the second protein; (2) a thirdrestriction endonuclease recognition site specific for a restrictionendonuclease that cleaves the nucleic acid sequence fragment distally tothe restriction endonuclease recognition site; and (3) a fourthrestriction endonuclease recognition site; thereby producing acombination; b) maintaining the combination under conditions in whichthe first protein and the second protein are expressed and interact; c)joining the first vector with the second vector, thereby forming acontiguous nucleic acid sequence that comprises: (i) the nucleic acidsequence that encodes a first protein that interacts with a secondprotein; (ii) the first restriction endonuclease recognition sitespecific for a restriction endonuclease that cleaves the nucleic acidsequence fragment distally to the restriction endonuclease recognitionsite; (iii) the second restriction endonuclease recognition site; (iv)the nucleic acid sequence that encodes the second protein; and (v) thethird restriction endonuclease recognition site specific for arestriction endonuclease that cleaves the nucleic acid sequence fragmentdistally to the restriction endonuclease recognition site; (vi) a fourthrestriction endonuclease recognition site; d) cleaving the secondrestriction endonuclease recognition site and the fourth restrictionendonuclease recognition site in the contiguous nucleic acid sequencewith restriction endonucleases, thereby producing compatible ends in thecontiguous nucleic acid sequence; e) maintaining the contiguous nucleicacid sequence under conditions in which the compatible ends in thecontiguous nucleic acid sequence intramolecularly ligate, therebyproducing a circularized nucleic acid sequence; f) cleaving the firstrestriction endonuclease recognition site and the third restrictionendonuclease recognition site in the circularized nucleic acid sequencewith restriction endonucleases that cleave the circularized nucleic acidsequence distally to the restriction endonuclease recognition sites,thereby producing a paired tag comprising a 5′ end tag and a 3′ end tagof the circularized nucleic acid sequence; and g) sequencing the pairedtag; thereby identifying nucleic acid sequences that encode at least twointeracting proteins.
 59. The method of claim 58, wherein the methodidentifies a plurality of nucleic acid sequences that encode at leasttwo interacting proteins, wherein the method comprises a plurality offirst vectors and a plurality of second vectors and wherein the methodfurther comprises the steps of: f′) joining the paired tags; and f″)sequencing the joined paired tags; thereby identifying a plurality ofnucleic acid sequences that encode at least two interacting proteins.60. The method of claim 54, wherein the joining step is site-specificintermolecular recombination. 61-62. (canceled)
 63. The method of claim57, wherein cleaving the second restriction endonuclease recognitionsite and cleaving the fourth restriction endonuclease recognition sitein the contiguous nucleic acid sequence releases a fragment containing arecombined site-specific recombinase recognition site between thenucleic acid sequence that encodes a sequence from the first protein anda sequence from the second protein that interact with each other. 64-69.(canceled)
 70. The method of claim 1, wherein step (a) is performed byemulsion ligation.
 71. The method of claim 17, wherein step (a) isperformed by emulsion ligation.
 72. The method of claim 18, wherein step(b) is performed by emulsion ligation.
 73. The method of claim 19,wherein steps (b) and (d) are performed by emulsion ligation.
 74. Themethod of claim 20, wherein steps (b) and (d) are performed by emulsionligation.
 75. The method of claim 46, wherein step (b) is performed byemulsion ligation.
 76. The method of claim 48, wherein the conditions inwhich the compatible ends intramolecularly ligate in step (d) areconditions suitable for emulsion ligation.
 77. The method of claim 51,wherein step (e) is performed by emulsion ligation.
 78. The method ofclaim 55, wherein step (d′) is performed by emulsion ligation.
 79. Themethod of claim 57, wherein the conditions in which the compatible endsin the contiguous nucleic acid sequence intramolecularly ligate in step(e) are conditions suitable for emulsion ligation.
 80. The method ofclaim 58, wherein the conditions in which the compatible ends in thecontiguous nucleic acid sequence intramolecularly ligate in step (e) areconditions suitable for emulsion ligation.
 81. The method of claim 59,where step (f′) is performed by emulsion ligation.